diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4f5e161f89..948f5d3bac 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,9 +1,47 @@
 name: CI
-on: [push, pull_request]
+on:
+  push:
+    branches: [ master ]
+  pull_request:
 permissions:
   contents: read # to fetch code (actions/checkout)
 jobs:
+  Setup:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 16
+          cache: npm
+      - run: npm install
+        env:
+          SKIP_PREPARE: true
+      - run: npm run build
+        env:
+          PUBLISH: true
+      - name: Upload build assets
+        id: upload-artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: build-assets
+          path: |
+            index.*
+            compiler.*
+            ssr.*
+            action/
+            animate/
+            easing/
+            internal/
+            motion/
+            store/
+            transition/
+            types/
   Tests:
+    needs: Setup
     runs-on: ${{ matrix.os }}
     timeout-minutes: 15
     strategy:
@@ -11,21 +49,28 @@ jobs:
         node-version: [8, 10, 12, 14, 16]
         os: [ubuntu-latest, windows-latest, macOS-latest]
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions/setup-node@v2
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
         with:
           node-version: ${{ matrix.node-version }}
           cache: npm
+      - name: Download build assets
+        uses: actions/download-artifact@v3
+        id: download-artifact
+        with:
+          name: build-assets
       - run: npm install
-      - run: npm test
+        env:
+          SKIP_PREPARE: true
+      - run: npm run test:integration
         env:
           CI: true
   Lint:
     runs-on: ubuntu-latest
     timeout-minutes: 5
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions/setup-node@v2
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
         with:
           cache: npm
       - run: 'npm i && npm run lint'
@@ -36,8 +81,11 @@ jobs:
       matrix:
         os: [ubuntu-latest, windows-latest, macOS-latest]
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions/setup-node@v2
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
         with:
           cache: npm
-      - run: 'npm i && npm run test:unit'
+      - run: npm install
+        env:
+          SKIP_PREPARE: true
+      - run: npm run test:unit
diff --git a/.mocharc.js b/.mocharc.js
index e55f26099e..449f81ecd6 100644
--- a/.mocharc.js
+++ b/.mocharc.js
@@ -1,7 +1,7 @@
+const is_unit_test = process.env.UNIT_TEST;
+
 module.exports = {
-	file: [
-		'test/test.ts'
-	],
+	file: is_unit_test ? [] : ['test/test.ts'],
 	require: [
 		'sucrase/register'
 	]
diff --git a/.mocharc.unit.js b/.mocharc.unit.js
new file mode 100644
index 0000000000..387d70e7e0
--- /dev/null
+++ b/.mocharc.unit.js
@@ -0,0 +1,15 @@
+module.exports = {
+	spec: [
+		'src/**/__test__.ts',
+	],
+	require: [
+		'sucrase/register'
+	],
+	recursive: true,
+};
+
+// add coverage options when running 'npx c8 mocha'
+if (process.env.NODE_V8_COVERAGE) {
+	module.exports.fullTrace = true;
+	module.exports.require.push('source-map-support/register');
+}
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d12212be87..cc41f14a88 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,25 +1,36 @@
 # Svelte changelog
 
 ## Unreleased
+* Upgraded `css-tree` to `2.1.0` ([#7572](https://github.com/sveltejs/svelte/pull/7572))
+
+## 3.52.0
+
+* Throw compile-time error when attempting to update `const` variable ([#4895](https://github.com/sveltejs/svelte/issues/4895))
+* Warn when using `<a target="_blank">` without `rel="noreferrer"` ([#6188](https://github.com/sveltejs/svelte/issues/6188))
+* Support `style:foo|important` modifier ([#7365](https://github.com/sveltejs/svelte/issues/7365))
+* Fix hydration regression with `{@html}` and components in `<svelte:head>` ([#7941](https://github.com/sveltejs/svelte/pull/7941))
+
+## 3.51.0
 
-* Fix hydration issue with using `{@html}` and components in `svelte:head` ([#4533](https://github.com/sveltejs/svelte/issues/4533), [#6463](https://github.com/sveltejs/svelte/issues/6463), [#7444](https://github.com/sveltejs/svelte/issues/7444))
-* Warn instead of throwing error if `<svelte:element>` is void tag ([#7566](https://github.com/sveltejs/svelte/issues/7566))
-* Treat `inert` as boolean attribute ([#7785](https://github.com/sveltejs/svelte/pull/7785))
-* Supporting scoped style for `<svelte:element>` ([#7443](https://github.com/sveltejs/svelte/issues/7443))
-* Supports SVG elements with `<svelte:element>`([#7613](https://github.com/sveltejs/svelte/issues/7613))
-* Warn user when binding on a `{...rest}` object in `{#each}` block ([#6860](https://github.com/sveltejs/svelte/issues/6860))
-* Supports `--style-props` for `<svelte:component>` ([#7461](https://github.com/sveltejs/svelte/issues/7461))
-* Supports `--style-props` for SVG components ([#7808](https://github.com/sveltejs/svelte/issues/7808))
 * Add a11y warnings:
-	* `a11y-no-noninteractive-tabindex`: check for tabindex on non-interactive elements ([#6693](https://github.com/sveltejs/svelte/pull/6693))
 	* `a11y-click-events-have-key-events`: check if click event is accompanied by key events ([#5073](https://github.com/sveltejs/svelte/pull/5073))
-* `a11y-role-has-required-aria-props` do not warn when elements matched their semantic role ([#7838](https://github.com/sveltejs/svelte/pull/7838))
-* Supports custom element in `<svelte:element>` ([#7766](https://github.com/sveltejs/svelte/pull/7766))
-* Improve performance of custom element data setting in `<svelte:element>` ([#7869](https://github.com/sveltejs/svelte/pull/7869))
+	* `a11y-no-noninteractive-tabindex`: check for tabindex on non-interactive elements ([#6693](https://github.com/sveltejs/svelte/pull/6693))
+* Warn when two-way binding to `{...rest}` object in `{#each}` block ([#6860](https://github.com/sveltejs/svelte/issues/6860))
+* Support `--style-props` on `<svelte:component>` ([#7461](https://github.com/sveltejs/svelte/issues/7461))
 * Supports nullish values for component event handlers ([#7568](https://github.com/sveltejs/svelte/issues/7568))
-* Better error message when specifying an invalid value for `<svelte:component this={...}>` ([#7550](https://github.com/sveltejs/svelte/issues/7550))
-* Fix to call component unmount if a component is mounted and then immediately unmounted ([#7817](https://github.com/sveltejs/svelte/issues/7817))
-* Fix false positive warnings about props binding in dev mode ([#4457](https://github.com/sveltejs/svelte/issues/4457))
+* Supports SVG elements with `<svelte:element>`([#7613](https://github.com/sveltejs/svelte/issues/7613))
+* Treat `inert` as boolean attribute ([#7785](https://github.com/sveltejs/svelte/pull/7785))
+* Support `--style-props` for SVG components ([#7808](https://github.com/sveltejs/svelte/issues/7808))
+* Fix false positive dev warnings about unset props when they are bound ([#4457](https://github.com/sveltejs/svelte/issues/4457))
+* Fix hydration with `{@html}` and components in `<svelte:head>` ([#4533](https://github.com/sveltejs/svelte/issues/4533), [#6463](https://github.com/sveltejs/svelte/issues/6463), [#7444](https://github.com/sveltejs/svelte/issues/7444))
+* Support scoped style for `<svelte:element>` ([#7443](https://github.com/sveltejs/svelte/issues/7443))
+* Improve error message for invalid value for `<svelte:component this={...}>` ([#7550](https://github.com/sveltejs/svelte/issues/7550))
+* Improve error message when using logic blocks or tags at invalid location ([#7552](https://github.com/sveltejs/svelte/issues/7552))
+* Warn instead of throwing error if `<svelte:element>` is a void tag ([#7566](https://github.com/sveltejs/svelte/issues/7566))
+* Supports custom elements in `<svelte:element>` ([#7733](https://github.com/sveltejs/svelte/issues/7733))
+* Fix calling component unmount if a component is mounted and then immediately unmounted ([#7817](https://github.com/sveltejs/svelte/issues/7817))
+* Do not generate `a11y-role-has-required-aria-props` warning when elements match their semantic role ([#7837](https://github.com/sveltejs/svelte/issues/7837))
+* Improve performance of custom element data setting in `<svelte:element>` ([#7869](https://github.com/sveltejs/svelte/pull/7869))
 
 ## 3.50.1
 
diff --git a/package-lock.json b/package-lock.json
index 23ccc6b66f..1e4763cac4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,18 +1,18 @@
 {
   "name": "svelte",
-  "version": "3.50.1",
+  "version": "3.52.0",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "svelte",
-      "version": "3.49.0",
+      "version": "3.52.0",
       "license": "MIT",
       "devDependencies": {
         "@ampproject/remapping": "^0.3.0",
         "@rollup/plugin-commonjs": "^11.0.0",
         "@rollup/plugin-json": "^4.0.1",
-        "@rollup/plugin-node-resolve": "^6.0.0",
+        "@rollup/plugin-node-resolve": "^11.2.1",
         "@rollup/plugin-replace": "^2.3.0",
         "@rollup/plugin-sucrase": "^3.1.0",
         "@rollup/plugin-typescript": "^2.0.1",
@@ -28,7 +28,7 @@
         "aria-query": "^5.0.0",
         "axobject-query": "^3.0.1",
         "code-red": "^0.2.5",
-        "css-tree": "^1.1.2",
+        "css-tree": "^2.1.0",
         "eslint": "^8.0.0",
         "eslint-plugin-import": "^2.26.0",
         "eslint-plugin-svelte3": "^4.0.0",
@@ -209,21 +209,54 @@
       }
     },
     "node_modules/@rollup/plugin-node-resolve": {
-      "version": "6.0.0",
-      "resolved": "https://registry.npmjs.org/@rollup/plugin-node-resolve/-/plugin-node-resolve-6.0.0.tgz",
-      "integrity": "sha512-GqWz1CfXOsqpeVMcoM315+O7zMxpRsmhWyhJoxLFHVSp9S64/u02i7len/FnbTNbmgYs+sZyilasijH8UiuboQ==",
+      "version": "11.2.1",
+      "resolved": "https://registry.npmjs.org/@rollup/plugin-node-resolve/-/plugin-node-resolve-11.2.1.tgz",
+      "integrity": "sha512-yc2n43jcqVyGE2sqV5/YCmocy9ArjVAP/BeXyTtADTBBX6V0e5UMqwO8CdQ0kzjb6zu5P1qMzsScCMRvE9OlVg==",
       "dev": true,
       "dependencies": {
-        "@rollup/pluginutils": "^3.0.0",
-        "@types/resolve": "0.0.8",
+        "@rollup/pluginutils": "^3.1.0",
+        "@types/resolve": "1.17.1",
         "builtin-modules": "^3.1.0",
+        "deepmerge": "^4.2.2",
         "is-module": "^1.0.0",
-        "resolve": "^1.11.1"
+        "resolve": "^1.19.0"
+      },
+      "engines": {
+        "node": ">= 10.0.0"
+      },
+      "peerDependencies": {
+        "rollup": "^1.20.0||^2.0.0"
+      }
+    },
+    "node_modules/@rollup/plugin-node-resolve/node_modules/@rollup/pluginutils": {
+      "version": "3.1.0",
+      "resolved": "https://registry.npmjs.org/@rollup/pluginutils/-/pluginutils-3.1.0.tgz",
+      "integrity": "sha512-GksZ6pr6TpIjHm8h9lSQ8pi8BE9VeubNT0OMJ3B5uZJ8pz73NPiqOtCog/x2/QzM1ENChPKxMDhiQuRHsqc+lg==",
+      "dev": true,
+      "dependencies": {
+        "@types/estree": "0.0.39",
+        "estree-walker": "^1.0.1",
+        "picomatch": "^2.2.2"
       },
       "engines": {
         "node": ">= 8.0.0"
+      },
+      "peerDependencies": {
+        "rollup": "^1.20.0||^2.0.0"
       }
     },
+    "node_modules/@rollup/plugin-node-resolve/node_modules/@types/estree": {
+      "version": "0.0.39",
+      "resolved": "https://registry.npmjs.org/@types/estree/-/estree-0.0.39.tgz",
+      "integrity": "sha512-EYNwp3bU+98cpU4lAWYYL7Zz+2gryWH1qbdDTidVd6hkiR6weksdbMadyXKXNPEkQFhXM+hVO9ZygomHXp+AIw==",
+      "dev": true
+    },
+    "node_modules/@rollup/plugin-node-resolve/node_modules/estree-walker": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/estree-walker/-/estree-walker-1.0.1.tgz",
+      "integrity": "sha512-1fMXF3YP4pZZVozF8j/ZLfvnR8NSIljt56UhbZ5PeeDmmGHpgpdwQt7ITlGvYaQukCvuBRMLEiKiYC+oeIg4cg==",
+      "dev": true
+    },
     "node_modules/@rollup/plugin-replace": {
       "version": "2.3.0",
       "resolved": "https://registry.npmjs.org/@rollup/plugin-replace/-/plugin-replace-2.3.0.tgz",
@@ -331,9 +364,9 @@
       "dev": true
     },
     "node_modules/@types/resolve": {
-      "version": "0.0.8",
-      "resolved": "https://registry.npmjs.org/@types/resolve/-/resolve-0.0.8.tgz",
-      "integrity": "sha512-auApPaJf3NPfe18hSoJkp8EbZzer2ISk7o8mCC3M9he/a04+gbMF97NkpD2S8riMGvm4BMRI59/SZQSaLTKpsQ==",
+      "version": "1.17.1",
+      "resolved": "https://registry.npmjs.org/@types/resolve/-/resolve-1.17.1.tgz",
+      "integrity": "sha512-yy7HuzQhj0dhGpD8RLXSZWEkLsV9ibvxvi6EiJ3bkqLAO1RGo0WbkWQiwpRlSFymTJRz0d3k5LM3kkx8ArDbLw==",
       "dev": true,
       "dependencies": {
         "@types/node": "*"
@@ -1077,25 +1110,17 @@
       "dev": true
     },
     "node_modules/css-tree": {
-      "version": "1.1.2",
-      "resolved": "https://registry.npmjs.org/css-tree/-/css-tree-1.1.2.tgz",
-      "integrity": "sha512-wCoWush5Aeo48GLhfHPbmvZs59Z+M7k5+B1xDnXbdWNcEF423DoFdqSWE0PM5aNk5nI5cp1q7ms36zGApY/sKQ==",
+      "version": "2.2.1",
+      "resolved": "https://registry.npmjs.org/css-tree/-/css-tree-2.2.1.tgz",
+      "integrity": "sha512-OA0mILzGc1kCOCSJerOeqDxDQ4HOh+G8NbOJFOTgOCzpw7fCBubk0fEyxp8AgOL/jvLgYA/uV0cMbe43ElF1JA==",
       "dev": true,
       "dependencies": {
-        "mdn-data": "2.0.14",
-        "source-map": "^0.6.1"
+        "mdn-data": "2.0.28",
+        "source-map-js": "^1.0.1"
       },
       "engines": {
-        "node": ">=8.0.0"
-      }
-    },
-    "node_modules/css-tree/node_modules/source-map": {
-      "version": "0.6.1",
-      "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
-      "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
-      "dev": true,
-      "engines": {
-        "node": ">=0.10.0"
+        "node": "^10 || ^12.20.0 || ^14.13.0 || >=15.0.0",
+        "npm": ">=7.0.0"
       }
     },
     "node_modules/cssom": {
@@ -1177,6 +1202,15 @@
       "integrity": "sha1-s2nW+128E+7PUk+RsHD+7cNXzzQ=",
       "dev": true
     },
+    "node_modules/deepmerge": {
+      "version": "4.2.2",
+      "resolved": "https://registry.npmjs.org/deepmerge/-/deepmerge-4.2.2.tgz",
+      "integrity": "sha512-FJ3UgI4gIl+PHZm53knsuSFpE+nESMr7M4v9QcgB7S63Kj/6WqMiFQJpBBYz1Pt+66bZpP3Q7Lye0Oo9MPKEdg==",
+      "dev": true,
+      "engines": {
+        "node": ">=0.10.0"
+      }
+    },
     "node_modules/define-properties": {
       "version": "1.1.4",
       "resolved": "https://registry.npmjs.org/define-properties/-/define-properties-1.1.4.tgz",
@@ -3108,9 +3142,9 @@
       }
     },
     "node_modules/mdn-data": {
-      "version": "2.0.14",
-      "resolved": "https://registry.npmjs.org/mdn-data/-/mdn-data-2.0.14.tgz",
-      "integrity": "sha512-dn6wd0uw5GsdswPFfsgMp5NSB0/aDe6fK94YJV/AJDYXL6HVLWBsxeq7js7Ad+mU2K9LAlwpk6kN2D5mwCPVow==",
+      "version": "2.0.28",
+      "resolved": "https://registry.npmjs.org/mdn-data/-/mdn-data-2.0.28.tgz",
+      "integrity": "sha512-aylIc7Z9y4yzHYAJNuESG3hfhC+0Ibp/MAMiaOZgNv4pmEdFyfZhhhny4MNiAfWdBQ1RQ2mfDWmM1x8SvGyp8g==",
       "dev": true
     },
     "node_modules/merge2": {
@@ -4055,6 +4089,15 @@
         "node": ">= 8"
       }
     },
+    "node_modules/source-map-js": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/source-map-js/-/source-map-js-1.0.2.tgz",
+      "integrity": "sha512-R0XvVJ9WusLiqTCEiGCmICCMplcCkIwwR11mOSD9CR5u+IXYdiseeEuXCVAjS54zqwkLcPNnmU4OeJ6tUrWhDw==",
+      "dev": true,
+      "engines": {
+        "node": ">=0.10.0"
+      }
+    },
     "node_modules/source-map-support": {
       "version": "0.5.13",
       "resolved": "https://registry.npmjs.org/source-map-support/-/source-map-support-0.5.13.tgz",
@@ -4884,16 +4927,42 @@
       }
     },
     "@rollup/plugin-node-resolve": {
-      "version": "6.0.0",
-      "resolved": "https://registry.npmjs.org/@rollup/plugin-node-resolve/-/plugin-node-resolve-6.0.0.tgz",
-      "integrity": "sha512-GqWz1CfXOsqpeVMcoM315+O7zMxpRsmhWyhJoxLFHVSp9S64/u02i7len/FnbTNbmgYs+sZyilasijH8UiuboQ==",
+      "version": "11.2.1",
+      "resolved": "https://registry.npmjs.org/@rollup/plugin-node-resolve/-/plugin-node-resolve-11.2.1.tgz",
+      "integrity": "sha512-yc2n43jcqVyGE2sqV5/YCmocy9ArjVAP/BeXyTtADTBBX6V0e5UMqwO8CdQ0kzjb6zu5P1qMzsScCMRvE9OlVg==",
       "dev": true,
       "requires": {
-        "@rollup/pluginutils": "^3.0.0",
-        "@types/resolve": "0.0.8",
+        "@rollup/pluginutils": "^3.1.0",
+        "@types/resolve": "1.17.1",
         "builtin-modules": "^3.1.0",
+        "deepmerge": "^4.2.2",
         "is-module": "^1.0.0",
-        "resolve": "^1.11.1"
+        "resolve": "^1.19.0"
+      },
+      "dependencies": {
+        "@rollup/pluginutils": {
+          "version": "3.1.0",
+          "resolved": "https://registry.npmjs.org/@rollup/pluginutils/-/pluginutils-3.1.0.tgz",
+          "integrity": "sha512-GksZ6pr6TpIjHm8h9lSQ8pi8BE9VeubNT0OMJ3B5uZJ8pz73NPiqOtCog/x2/QzM1ENChPKxMDhiQuRHsqc+lg==",
+          "dev": true,
+          "requires": {
+            "@types/estree": "0.0.39",
+            "estree-walker": "^1.0.1",
+            "picomatch": "^2.2.2"
+          }
+        },
+        "@types/estree": {
+          "version": "0.0.39",
+          "resolved": "https://registry.npmjs.org/@types/estree/-/estree-0.0.39.tgz",
+          "integrity": "sha512-EYNwp3bU+98cpU4lAWYYL7Zz+2gryWH1qbdDTidVd6hkiR6weksdbMadyXKXNPEkQFhXM+hVO9ZygomHXp+AIw==",
+          "dev": true
+        },
+        "estree-walker": {
+          "version": "1.0.1",
+          "resolved": "https://registry.npmjs.org/estree-walker/-/estree-walker-1.0.1.tgz",
+          "integrity": "sha512-1fMXF3YP4pZZVozF8j/ZLfvnR8NSIljt56UhbZ5PeeDmmGHpgpdwQt7ITlGvYaQukCvuBRMLEiKiYC+oeIg4cg==",
+          "dev": true
+        }
       }
     },
     "@rollup/plugin-replace": {
@@ -4997,9 +5066,9 @@
       "dev": true
     },
     "@types/resolve": {
-      "version": "0.0.8",
-      "resolved": "https://registry.npmjs.org/@types/resolve/-/resolve-0.0.8.tgz",
-      "integrity": "sha512-auApPaJf3NPfe18hSoJkp8EbZzer2ISk7o8mCC3M9he/a04+gbMF97NkpD2S8riMGvm4BMRI59/SZQSaLTKpsQ==",
+      "version": "1.17.1",
+      "resolved": "https://registry.npmjs.org/@types/resolve/-/resolve-1.17.1.tgz",
+      "integrity": "sha512-yy7HuzQhj0dhGpD8RLXSZWEkLsV9ibvxvi6EiJ3bkqLAO1RGo0WbkWQiwpRlSFymTJRz0d3k5LM3kkx8ArDbLw==",
       "dev": true,
       "requires": {
         "@types/node": "*"
@@ -5545,21 +5614,13 @@
       "dev": true
     },
     "css-tree": {
-      "version": "1.1.2",
-      "resolved": "https://registry.npmjs.org/css-tree/-/css-tree-1.1.2.tgz",
-      "integrity": "sha512-wCoWush5Aeo48GLhfHPbmvZs59Z+M7k5+B1xDnXbdWNcEF423DoFdqSWE0PM5aNk5nI5cp1q7ms36zGApY/sKQ==",
+      "version": "2.2.1",
+      "resolved": "https://registry.npmjs.org/css-tree/-/css-tree-2.2.1.tgz",
+      "integrity": "sha512-OA0mILzGc1kCOCSJerOeqDxDQ4HOh+G8NbOJFOTgOCzpw7fCBubk0fEyxp8AgOL/jvLgYA/uV0cMbe43ElF1JA==",
       "dev": true,
       "requires": {
-        "mdn-data": "2.0.14",
-        "source-map": "^0.6.1"
-      },
-      "dependencies": {
-        "source-map": {
-          "version": "0.6.1",
-          "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
-          "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
-          "dev": true
-        }
+        "mdn-data": "2.0.28",
+        "source-map-js": "^1.0.1"
       }
     },
     "cssom": {
@@ -5626,6 +5687,12 @@
       "integrity": "sha1-s2nW+128E+7PUk+RsHD+7cNXzzQ=",
       "dev": true
     },
+    "deepmerge": {
+      "version": "4.2.2",
+      "resolved": "https://registry.npmjs.org/deepmerge/-/deepmerge-4.2.2.tgz",
+      "integrity": "sha512-FJ3UgI4gIl+PHZm53knsuSFpE+nESMr7M4v9QcgB7S63Kj/6WqMiFQJpBBYz1Pt+66bZpP3Q7Lye0Oo9MPKEdg==",
+      "dev": true
+    },
     "define-properties": {
       "version": "1.1.4",
       "resolved": "https://registry.npmjs.org/define-properties/-/define-properties-1.1.4.tgz",
@@ -7103,9 +7170,9 @@
       }
     },
     "mdn-data": {
-      "version": "2.0.14",
-      "resolved": "https://registry.npmjs.org/mdn-data/-/mdn-data-2.0.14.tgz",
-      "integrity": "sha512-dn6wd0uw5GsdswPFfsgMp5NSB0/aDe6fK94YJV/AJDYXL6HVLWBsxeq7js7Ad+mU2K9LAlwpk6kN2D5mwCPVow==",
+      "version": "2.0.28",
+      "resolved": "https://registry.npmjs.org/mdn-data/-/mdn-data-2.0.28.tgz",
+      "integrity": "sha512-aylIc7Z9y4yzHYAJNuESG3hfhC+0Ibp/MAMiaOZgNv4pmEdFyfZhhhny4MNiAfWdBQ1RQ2mfDWmM1x8SvGyp8g==",
       "dev": true
     },
     "merge2": {
@@ -7837,6 +7904,12 @@
       "integrity": "sha512-l3BikUxvPOcn5E74dZiq5BGsTb5yEwhaTSzccU6t4sDOH8NWJCstKO5QT2CvtFoK6F0saL7p9xHAqHOlCPJygA==",
       "dev": true
     },
+    "source-map-js": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/source-map-js/-/source-map-js-1.0.2.tgz",
+      "integrity": "sha512-R0XvVJ9WusLiqTCEiGCmICCMplcCkIwwR11mOSD9CR5u+IXYdiseeEuXCVAjS54zqwkLcPNnmU4OeJ6tUrWhDw==",
+      "dev": true
+    },
     "source-map-support": {
       "version": "0.5.13",
       "resolved": "https://registry.npmjs.org/source-map-support/-/source-map-support-0.5.13.tgz",
diff --git a/package.json b/package.json
index 836fa33267..245c9b1834 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "svelte",
-  "version": "3.50.1",
+  "version": "3.52.0",
   "description": "Cybernetically enhanced web apps",
   "module": "index.mjs",
   "main": "index",
@@ -86,15 +86,15 @@
   },
   "types": "types/runtime/index.d.ts",
   "scripts": {
-    "test": "mocha --exit",
-    "test:unit": "mocha --require sucrase/register --recursive src/**/__test__.ts --exit",
-    "quicktest": "mocha",
+    "test": "npm run test:unit && npm run test:integration",
+    "test:integration": "mocha --exit",
+    "test:unit": "mocha --config .mocharc.unit.js --exit",
+    "quicktest": "mocha --exit",
     "build": "rollup -c && npm run tsd",
-    "prepare": "npm run build",
+    "prepare": "node scripts/skip_in_ci.js npm run build",
     "dev": "rollup -cw",
-    "pretest": "npm run build",
     "posttest": "agadoo internal/index.mjs",
-    "prepublishOnly": "node check_publish_env.js && npm run lint && npm test",
+    "prepublishOnly": "node check_publish_env.js && npm run lint && npm run build && npm test",
     "tsd": "node ./generate-type-definitions.js",
     "lint": "eslint \"{src,test}/**/*.{ts,js}\""
   },
@@ -118,7 +118,7 @@
     "@ampproject/remapping": "^0.3.0",
     "@rollup/plugin-commonjs": "^11.0.0",
     "@rollup/plugin-json": "^4.0.1",
-    "@rollup/plugin-node-resolve": "^6.0.0",
+    "@rollup/plugin-node-resolve": "^11.2.1",
     "@rollup/plugin-replace": "^2.3.0",
     "@rollup/plugin-sucrase": "^3.1.0",
     "@rollup/plugin-typescript": "^2.0.1",
@@ -134,7 +134,7 @@
     "aria-query": "^5.0.0",
     "axobject-query": "^3.0.1",
     "code-red": "^0.2.5",
-    "css-tree": "^1.1.2",
+    "css-tree": "^2.1.0",
     "eslint": "^8.0.0",
     "eslint-plugin-import": "^2.26.0",
     "eslint-plugin-svelte3": "^4.0.0",
diff --git a/scripts/skip_in_ci.js b/scripts/skip_in_ci.js
new file mode 100644
index 0000000000..d845d000ab
--- /dev/null
+++ b/scripts/skip_in_ci.js
@@ -0,0 +1,7 @@
+if (process.env.SKIP_PREPARE) {
+  console.log('Skipped "prepare" script');
+} else {
+	const { execSync } = require("child_process");
+	const command = process.argv.slice(2).join(" ");
+	execSync(command, { stdio: "inherit" });
+}
diff --git a/site/content/docs/01-getting-started.md b/site/content/docs/01-getting-started.md
index 8ae5b1fb9c..48cdbcc231 100644
--- a/site/content/docs/01-getting-started.md
+++ b/site/content/docs/01-getting-started.md
@@ -7,6 +7,7 @@ title: Getting started
 To try Svelte in an interactive online environment you can try [the REPL](https://svelte.dev/repl) or [StackBlitz](https://node.new/svelte).
 
 To create a project locally, run:
+
 ```
 npm create vite@latest myapp -- --template svelte
 cd myapp
@@ -14,8 +15,8 @@ npm install
 npm run dev
 ```
 
-Or use [SvelteKit](https://kit.svelte.dev/), the official application framework from the Svelte team (currently in beta).
+Or use [SvelteKit](https://kit.svelte.dev/), the official application framework from the Svelte team (currently in release candidate status).
 
-See the SvelteSociety website run by the Svelte community for a list of integrations with various [tooling and editots](https://sveltesociety.dev/tools).
+The Svelte team maintains a [VS Code extension](https://marketplace.visualstudio.com/items?itemName=svelte.svelte-vscode) and the Svelte community has created a list of integrations with various other [tooling and editors](https://sveltesociety.dev/tools).
 
 If you're having trouble, get help on [Discord](https://svelte.dev/chat) or [StackOverflow](https://stackoverflow.com/questions/tagged/svelte).
diff --git a/site/content/docs/02-component-format.md b/site/content/docs/02-component-format.md
index 5212b001ac..268444ab7d 100644
--- a/site/content/docs/02-component-format.md
+++ b/site/content/docs/02-component-format.md
@@ -209,7 +209,7 @@ It is important to note that the reactive blocks are ordered via simple static a
 </script>
 ```
 
-Moving the line `$: yDependent = y` bellow `$: setY(x)` will cause `yDependent` to be updated when `x` is updated.
+Moving the line `$: yDependent = y` below `$: setY(x)` will cause `yDependent` to be updated when `x` is updated.
 
 ---
 
diff --git a/site/content/docs/03-template-syntax.md b/site/content/docs/03-template-syntax.md
index 24b6111fae..9afe399469 100644
--- a/site/content/docs/03-template-syntax.md
+++ b/site/content/docs/03-template-syntax.md
@@ -158,7 +158,7 @@ You can use HTML comments inside components.
 
 ---
 
-Comments beginning with `svelte-ignore` disable warnings for the next block of markup. Usually these are accessibility warnings; make sure that you're disabling them for a good reason.
+Comments beginning with `svelte-ignore` disable warnings for the next block of markup. Usually, these are accessibility warnings; make sure that you're disabling them for a good reason.
 
 ```sv
 <!-- svelte-ignore a11y-autofocus -->
@@ -593,7 +593,7 @@ The simplest bindings reflect the value of a property, such as `input.value`.
 
 ---
 
-If the name matches the value, you can use a shorthand.
+If the name matches the value, you can use shorthand.
 
 ```sv
 <!-- These are equivalent -->
@@ -750,7 +750,7 @@ Videos additionally have readonly `videoWidth` and `videoHeight` bindings.
 
 ---
 
-Block-level elements have 4 readonly bindings, measured using a technique similar to [this one](http://www.backalleycoder.com/2013/03/18/cross-browser-event-based-element-resize-detection/):
+Block-level elements have 4 read-only bindings, measured using a technique similar to [this one](http://www.backalleycoder.com/2013/03/18/cross-browser-event-based-element-resize-detection/):
 
 * `clientWidth`
 * `clientHeight`
@@ -874,6 +874,9 @@ The `style:` directive provides a shorthand for setting multiple styles on an el
 
 <!-- Multiple styles can be included -->
 <div style:color style:width="12rem" style:background-color={darkMode ? "black" : "white"}>...</div>
+
+<!-- Styles can be marked as important -->
+<div style:color|important="red">...</div>
 ```
 
 ---
@@ -981,7 +984,7 @@ transition = (node: HTMLElement, params: any) => {
 
 A transition is triggered by an element entering or leaving the DOM as a result of a state change.
 
-When a block is transitioning out, all elements inside the block, including those that do not have their own transitions, are kept in the DOM until every transition in the block has completed.
+When a block is transitioning out, all elements inside the block, including those that do not have their own transitions, are kept in the DOM until every transition in the block has been completed.
 
 The `transition:` directive indicates a *bidirectional* transition, which means it can be smoothly reversed while the transition is in progress.
 
@@ -1241,7 +1244,7 @@ As with actions and transitions, animations can have parameters.
 
 ---
 
-Animations can use custom functions that provide the `node`, an `animation` object and any `parameters` as arguments. The `animation` parameter is an object containing `from` and `to` properties each containing a [DOMRect](https://developer.mozilla.org/en-US/docs/Web/API/DOMRect#Properties) describing the geometry of the element in its `start` and `end` positions. The `from` property is the DOMRect of the element in its starting position, the `to` property is the DOMRect of the element in its final position after the list has been reordered and the DOM updated.
+Animations can use custom functions that provide the `node`, an `animation` object and any `parameters` as arguments. The `animation` parameter is an object containing `from` and `to` properties each containing a [DOMRect](https://developer.mozilla.org/en-US/docs/Web/API/DOMRect#Properties) describing the geometry of the element in its `start` and `end` positions. The `from` property is the DOMRect of the element in its starting position, and the `to` property is the DOMRect of the element in its final position after the list has been reordered and the DOM updated.
 
 If the returned object has a `css` method, Svelte will create a CSS animation that plays on the element.
 
@@ -1390,7 +1393,7 @@ For SVG namespace, the example above desugars into using `<g>` instead:
 
 ---
 
-Svelte's CSS Variables support allows for easily themable components:
+Svelte's CSS Variables support allows for easily themeable components:
 
 ```sv
 <!-- Slider.svelte -->
@@ -1654,7 +1657,7 @@ If `this` is falsy, no component is rendered.
 
 The `<svelte:element>` element lets you render an element of a dynamically specified type. This is useful for example when displaying rich text content from a CMS. Any properties and event listeners present will be applied to the element.
 
-The only supported binding is `bind:this`, since the element type specific bindings that Svelte does at build time (e.g. `bind:value` for input elements) does not work with a dynamic tag type.
+The only supported binding is `bind:this`, since the element type specific bindings that Svelte does at build time (e.g. `bind:value` for input elements) do not work with a dynamic tag type.
 
 If `this` has a nullish value, the element and its children will not be rendered.
 
diff --git a/site/content/docs/06-accessibility-warnings.md b/site/content/docs/06-accessibility-warnings.md
index c82ef21fcb..8be8eb888c 100644
--- a/site/content/docs/06-accessibility-warnings.md
+++ b/site/content/docs/06-accessibility-warnings.md
@@ -268,7 +268,7 @@ Some HTML elements have default ARIA roles. Giving these elements an ARIA role t
 Tab key navigation should be limited to elements on the page that can be interacted with.
 
 ```sv
-<!-- A11y: not interactive element cannot have positive tabIndex value -->
+<!-- A11y: noninteractive element cannot have positive tabIndex value -->
 <div tabindex='0' />
 ```
 
diff --git a/site/content/examples/03-logic/03-each-blocks/App.svelte b/site/content/examples/03-logic/03-each-blocks/App.svelte
index 3ecbe5ca2f..7d08b79ab8 100644
--- a/site/content/examples/03-logic/03-each-blocks/App.svelte
+++ b/site/content/examples/03-logic/03-each-blocks/App.svelte
@@ -11,7 +11,7 @@
 <ul>
 	{#each cats as { id, name }, i}
 		<li>
-			<a target="_blank" href="https://www.youtube.com/watch?v={id}">
+			<a target="_blank" rel="noreferrer" href="https://www.youtube.com/watch?v={id}">
 				{i + 1}: {name}
 			</a>
 		</li>
diff --git a/site/content/examples/15-composition/03-slot-props/App.svelte b/site/content/examples/15-composition/03-slot-props/App.svelte
index 299cd336a6..5525867932 100644
--- a/site/content/examples/15-composition/03-slot-props/App.svelte
+++ b/site/content/examples/15-composition/03-slot-props/App.svelte
@@ -43,4 +43,8 @@
 		background-color: #ff3e00;
 		color: white;
 	}
-</style>
\ No newline at end of file
+	
+	p {
+		pointer-events: none;
+	}
+</style>
diff --git a/src/compiler/compile/Component.ts b/src/compiler/compile/Component.ts
index 2f8874de7a..c0d703892b 100644
--- a/src/compiler/compile/Component.ts
+++ b/src/compiler/compile/Component.ts
@@ -47,6 +47,10 @@ interface ComponentOptions {
 	preserveWhitespace?: boolean;
 }
 
+const regex_leading_directory_separator = /^[/\\]/;
+const regex_starts_with_term_export = /^Export/;
+const regex_contains_term_function = /Function/;
+
 export default class Component {
 	stats: Stats;
 	warnings: Warning[];
@@ -136,7 +140,7 @@ export default class Component {
 			(typeof process !== 'undefined'
 				? compile_options.filename
 					.replace(process.cwd(), '')
-					.replace(/^[/\\]/, '')
+					.replace(regex_leading_directory_separator, '')
 				: compile_options.filename);
 		this.locate = getLocator(this.source, { offsetLine: 1 });
 
@@ -638,7 +642,7 @@ export default class Component {
 				body.splice(i, 1);
 			}
 
-			if (/^Export/.test(node.type)) {
+			if (regex_starts_with_term_export.test(node.type)) {
 				const replacement = this.extract_exports(node, true);
 				if (replacement) {
 					body[i] = replacement;
@@ -788,6 +792,42 @@ export default class Component {
 					scope = map.get(node);
 				}
 
+				let deep = false;
+				let names: string[] | undefined; 
+
+				if (node.type === 'AssignmentExpression') {
+					deep = node.left.type === 'MemberExpression';
+					names = deep
+						? [get_object(node.left).name]
+						: extract_names(node.left);
+				} else if (node.type === 'UpdateExpression') {
+					deep = node.argument.type === 'MemberExpression';
+					const { name } = get_object(node.argument);
+					names = [name];
+				}
+
+				if (names) {
+					names.forEach(name => {
+						let current_scope = scope;
+						let declaration;
+
+						while (current_scope) {
+							if (current_scope.declarations.has(name)) {
+								declaration = current_scope.declarations.get(name);
+								break;
+							}
+							current_scope = current_scope.parent;
+						}
+
+						if (declaration && declaration.kind === 'const' && !deep) {
+							component.error(node as any, {
+								code: 'assignment-to-const',
+								message: 'You are assigning to a const'
+							});
+						}
+					});
+				}
+
 				if (node.type === 'ImportDeclaration') {
 					component.extract_imports(node);
 					// TODO: to use actual remove
@@ -795,7 +835,7 @@ export default class Component {
 					return this.skip();
 				}
 
-				if (/^Export/.test(node.type)) {
+				if (regex_starts_with_term_export.test(node.type)) {
 					const replacement = component.extract_exports(node);
 					if (replacement) {
 						this.replace(replacement);
@@ -918,7 +958,7 @@ export default class Component {
 				}
 
 				if (name[1] !== '$' && scope.has(name.slice(1)) && scope.find_owner(name.slice(1)) !== this.instance_scope) {
-					if (!((/Function/.test(parent.type) && prop === 'params') || (parent.type === 'VariableDeclarator' && prop === 'id'))) {
+					if (!((regex_contains_term_function.test(parent.type) && prop === 'params') || (parent.type === 'VariableDeclarator' && prop === 'id'))) {
 						return this.error(node as any, compiler_errors.contextual_store);
 					}
 				}
@@ -965,7 +1005,7 @@ export default class Component {
 
 		walk(this.ast.instance.content, {
 			enter(node: Node) {
-				if (/Function/.test(node.type)) {
+				if (regex_contains_term_function.test(node.type)) {
 					return this.skip();
 				}
 
@@ -1089,7 +1129,7 @@ export default class Component {
 
 						this.replace(b`
 							${node.declarations.length ? node : null}
-							${ props.length > 0 && b`let { ${ props } } = $$props;`}
+							${ props.length > 0 && b`let { ${props} } = $$props;`}
 							${inserts}
 						` as any);
 						return this.skip();
@@ -1460,6 +1500,8 @@ export default class Component {
 	}
 }
 
+const regex_valid_tag_name = /^[a-zA-Z][a-zA-Z0-9]*-[a-zA-Z0-9-]+$/;
+
 function process_component_options(component: Component, nodes) {
 	const component_options: ComponentOptions = {
 		immutable: component.compile_options.immutable || false,
@@ -1473,7 +1515,7 @@ function process_component_options(component: Component, nodes) {
 
 	const node = nodes.find(node => node.name === 'svelte:options');
 
-	function get_value(attribute, {code, message}) {
+	function get_value(attribute, { code, message }) {
 		const { value } = attribute;
 		const chunk = value[0];
 
@@ -1505,7 +1547,7 @@ function process_component_options(component: Component, nodes) {
 							return component.error(attribute, compiler_errors.invalid_tag_attribute);
 						}
 
-						if (tag && !/^[a-zA-Z][a-zA-Z0-9]*-[a-zA-Z0-9-]+$/.test(tag)) {
+						if (tag && !regex_valid_tag_name.test(tag)) {
 							return component.error(attribute, compiler_errors.invalid_tag_property);
 						}
 
diff --git a/src/compiler/compile/compiler_errors.ts b/src/compiler/compile/compiler_errors.ts
index c1a7d8bc5c..e4d4ffddad 100644
--- a/src/compiler/compile/compiler_errors.ts
+++ b/src/compiler/compile/compiler_errors.ts
@@ -281,5 +281,9 @@ export default {
 	invalid_component_style_directive: {
 		code: 'invalid-component-style-directive',
 		message: 'Style directives cannot be used on components'
-	}
+	},
+	invalid_style_directive_modifier: (valid: string) => ({
+		code: 'invalid-style-directive-modifier',
+		message: `Valid modifiers for style directives are: ${valid}`
+	})
 };
diff --git a/src/compiler/compile/compiler_warnings.ts b/src/compiler/compile/compiler_warnings.ts
index f194090870..3a11e04bd1 100644
--- a/src/compiler/compile/compiler_warnings.ts
+++ b/src/compiler/compile/compiler_warnings.ts
@@ -185,7 +185,7 @@ export default {
 	}),
 	a11y_no_noninteractive_tabindex: {
 		code: 'a11y-no-noninteractive-tabindex',
-		message: 'A11y: not interactive element cannot have positive tabIndex value'
+		message: 'A11y: noninteractive element cannot have positive tabIndex value'
 	},
 	redundant_event_modifier_for_touch: {
 		code: 'redundant-event-modifier',
diff --git a/src/compiler/compile/css/Selector.ts b/src/compiler/compile/css/Selector.ts
index 17302c4abd..07e2dc439e 100644
--- a/src/compiler/compile/css/Selector.ts
+++ b/src/compiler/compile/css/Selector.ts
@@ -9,6 +9,7 @@ import EachBlock from '../nodes/EachBlock';
 import IfBlock from '../nodes/IfBlock';
 import AwaitBlock from '../nodes/AwaitBlock';
 import compiler_errors from '../compiler_errors';
+import { regex_starts_with_whitespace, regex_ends_with_whitespace } from '../../utils/patterns';
 
 enum BlockAppliesToNode {
 	NotPossible,
@@ -25,6 +26,8 @@ const whitelist_attribute_selector = new Map([
 	['dialog', new Set(['open'])]
 ]);
 
+const regex_is_single_css_selector = /[^\\],(?!([^([]+[^\\]|[^([\\])[)\]])/;
+
 export default class Selector {
 	node: CssNode;
 	stylesheet: Stylesheet;
@@ -157,7 +160,7 @@ export default class Selector {
 		for (const block of this.blocks) {
 			for (const selector of block.selectors) {
 				if (selector.type === 'PseudoClassSelector' && selector.name === 'global') {
-					if (/[^\\],(?!([^([]+[^\\]|[^([\\])[)\]])/.test(selector.children[0].value)) {
+					if (regex_is_single_css_selector.test(selector.children[0].value)) {
 						component.error(selector, compiler_errors.css_invalid_global_selector);
 					}
 				}
@@ -209,7 +212,7 @@ function apply_selector(blocks: Block[], node: Element, to_encapsulate: Array<{
 	}
 
 	if (block.combinator) {
-		if (block.combinator.type === 'WhiteSpace') {
+		if (block.combinator.type === 'Combinator' && block.combinator.name === ' ') {
 			for (const ancestor_block of blocks) {
 				if (ancestor_block.global) {
 					continue;
@@ -281,12 +284,14 @@ function apply_selector(blocks: Block[], node: Element, to_encapsulate: Array<{
 	return true;
 }
 
+const regex_backslash_and_following_character = /\\(.)/g;
+
 function block_might_apply_to_node(block: Block, node: Element): BlockAppliesToNode {
 	let i = block.selectors.length;
 
 	while (i--) {
 		const selector = block.selectors[i];
-		const name = typeof selector.name === 'string' && selector.name.replace(/\\(.)/g, '$1');
+		const name = typeof selector.name === 'string' && selector.name.replace(regex_backslash_and_following_character, '$1');
 
 		if (selector.type === 'PseudoClassSelector' && (name === 'host' || name === 'root')) {
 			return BlockAppliesToNode.NotPossible;
@@ -371,7 +376,7 @@ function attribute_matches(node: CssNode, name: string, expected_value: string,
 			const start_with_space = [];
 			const remaining = [];
 			current_possible_values.forEach((current_possible_value: string) => {
-				if (/^\s/.test(current_possible_value)) {
+				if (regex_starts_with_whitespace.test(current_possible_value)) {
 					start_with_space.push(current_possible_value);
 				} else {
 					remaining.push(current_possible_value);
@@ -392,7 +397,7 @@ function attribute_matches(node: CssNode, name: string, expected_value: string,
 				prev_values = combined;
 
 				start_with_space.forEach((value: string) => {
-					if (/\s$/.test(value)) {
+					if (regex_ends_with_whitespace.test(value)) {
 						possible_values.add(value);
 					} else {
 						prev_values.push(value);
@@ -406,7 +411,7 @@ function attribute_matches(node: CssNode, name: string, expected_value: string,
 		}
 
 		current_possible_values.forEach((current_possible_value: string) => {
-			if (/\s$/.test(current_possible_value)) {
+			if (regex_ends_with_whitespace.test(current_possible_value)) {
 				possible_values.add(current_possible_value);
 			} else {
 				prev_values.push(current_possible_value);
diff --git a/src/compiler/compile/css/Stylesheet.ts b/src/compiler/compile/css/Stylesheet.ts
index 1a9ea7feeb..9a3cbe9d13 100644
--- a/src/compiler/compile/css/Stylesheet.ts
+++ b/src/compiler/compile/css/Stylesheet.ts
@@ -9,9 +9,12 @@ import hash from '../utils/hash';
 import compiler_warnings from '../compiler_warnings';
 import { extract_ignores_above_position } from '../../utils/extract_svelte_ignore';
 import { push_array } from '../../utils/push_array';
+import { regex_only_whitespaces, regex_whitespace } from '../../utils/patterns';
+
+const regex_css_browser_prefix = /^-((webkit)|(moz)|(o)|(ms))-/;
 
 function remove_css_prefix(name: string): string {
-	return name.replace(/^-((webkit)|(moz)|(o)|(ms))-/, '');
+	return name.replace(regex_css_browser_prefix, '');
 }
 
 const is_keyframes_node = (node: CssNode) =>
@@ -147,10 +150,10 @@ class Declaration {
 
 		// Don't minify whitespace in custom properties, since some browsers (Chromium < 99)
 		// treat --foo: ; and --foo:; differently
-		if (first.type === 'Raw' && /^\s+$/.test(first.value)) return;
+		if (first.type === 'Raw' && regex_only_whitespaces.test(first.value)) return;
 
 		let start = first.start;
-		while (/\s/.test(code.original[start])) start += 1;
+		while (regex_whitespace.test(code.original[start])) start += 1;
 
 		if (start - c > 1) {
 			code.overwrite(c, start, ':');
diff --git a/src/compiler/compile/index.ts b/src/compiler/compile/index.ts
index ceae02a1f0..38a3da057c 100644
--- a/src/compiler/compile/index.ts
+++ b/src/compiler/compile/index.ts
@@ -43,6 +43,9 @@ const valid_css_values = [
 	'none'
 ];
 
+const regex_valid_identifier = /^[a-zA-Z_$][a-zA-Z_$0-9]*$/;
+const regex_starts_with_lowercase_character = /^[a-z]/;
+
 function validate_options(options: CompileOptions, warnings: Warning[]) {
 	const { name, filename, loopGuardTimeout, dev, namespace, css } = options;
 
@@ -56,11 +59,11 @@ function validate_options(options: CompileOptions, warnings: Warning[]) {
 		}
 	});
 
-	if (name && !/^[a-zA-Z_$][a-zA-Z_$0-9]*$/.test(name)) {
+	if (name && !regex_valid_identifier.test(name)) {
 		throw new Error(`options.name must be a valid identifier (got '${name}')`);
 	}
 
-	if (name && /^[a-z]/.test(name)) {
+	if (name && regex_starts_with_lowercase_character.test(name)) {
 		const message = 'options.name should be capitalised';
 		warnings.push({
 			code: 'options-lowercase-name',
diff --git a/src/compiler/compile/nodes/Binding.ts b/src/compiler/compile/nodes/Binding.ts
index 594490a5fb..f826df4828 100644
--- a/src/compiler/compile/nodes/Binding.ts
+++ b/src/compiler/compile/nodes/Binding.ts
@@ -3,7 +3,7 @@ import get_object from '../utils/get_object';
 import Expression from './shared/Expression';
 import Component from '../Component';
 import TemplateScope from './shared/TemplateScope';
-import {dimensions} from '../../utils/patterns';
+import { regex_dimensions } from '../../utils/patterns';
 import { Node as ESTreeNode } from 'estree';
 import { TemplateNode } from '../../interfaces';
 import Element from './Element';
@@ -88,7 +88,7 @@ export default class Binding extends Node {
 		const type = parent.get_static_attribute_value('type');
 
 		this.is_readonly =
-			dimensions.test(this.name) ||
+			regex_dimensions.test(this.name) ||
 			(isElement(parent) &&
 				((parent.is_media_node() && read_only_media_attributes.has(this.name)) ||
 					(parent.name === 'input' && type === 'file')) /* TODO others? */);
diff --git a/src/compiler/compile/nodes/Element.ts b/src/compiler/compile/nodes/Element.ts
index 79f2800437..298276c437 100644
--- a/src/compiler/compile/nodes/Element.ts
+++ b/src/compiler/compile/nodes/Element.ts
@@ -11,7 +11,7 @@ import StyleDirective from './StyleDirective';
 import Text from './Text';
 import { namespaces } from '../../utils/namespaces';
 import map_children from './shared/map_children';
-import { dimensions, start_newline } from '../../utils/patterns';
+import { regex_dimensions, regex_starts_with_newline, regex_non_whitespace_character } from '../../utils/patterns';
 import fuzzymatch from '../../utils/fuzzymatch';
 import list from '../../utils/list';
 import Let from './Let';
@@ -203,6 +203,10 @@ function is_valid_aria_attribute_value(schema: ARIAPropertyDefinition, value: st
 	}
 }
 
+const regex_any_repeated_whitespaces = /[\s]+/g;
+const regex_heading_tags = /^h[1-6]$/;
+const regex_illegal_attribute_character = /(^[0-9-.])|[\^$@%&#?!|()[\]{}^*+~;]/;
+
 export default class Element extends Node {
 	type: 'Element';
 	name: string;
@@ -253,7 +257,7 @@ export default class Element extends Node {
 					// places if there's another newline afterwards.
 					// see https://html.spec.whatwg.org/multipage/syntax.html#element-restrictions
 					// see https://html.spec.whatwg.org/multipage/grouping-content.html#the-pre-element
-					first.data = first.data.replace(start_newline, '');
+					first.data = first.data.replace(regex_starts_with_newline, '');
 				}
 			}
 
@@ -398,7 +402,7 @@ export default class Element extends Node {
 
 			// Errors
 
-			if (/(^[0-9-.])|[\^$@%&#?!|()[\]{}^*+~;]/.test(name)) {
+			if (regex_illegal_attribute_character.test(name)) {
 				return component.error(attribute, compiler_errors.illegal_attribute(name));
 			}
 
@@ -464,7 +468,7 @@ export default class Element extends Node {
 					component.warn(attribute, compiler_warnings.a11y_unknown_aria_attribute(type, match));
 				}
 
-				if (name === 'aria-hidden' && /^h[1-6]$/.test(this.name)) {
+				if (name === 'aria-hidden' && regex_heading_tags.test(this.name)) {
 					component.warn(attribute, compiler_warnings.a11y_hidden(this.name));
 				}
 
@@ -609,6 +613,26 @@ export default class Element extends Node {
 			const href_attribute = attribute_map.get('href') || attribute_map.get('xlink:href');
 			const id_attribute = attribute_map.get('id');
 			const name_attribute = attribute_map.get('name');
+			const target_attribute = attribute_map.get('target');
+
+			if (target_attribute && target_attribute.get_static_value() === '_blank' && href_attribute) {
+				const href_static_value = href_attribute.get_static_value() ? href_attribute.get_static_value().toLowerCase() : null;
+
+				if (href_static_value === null || href_static_value.match(/^(https?:)?\/\//i)) {
+					const rel = attribute_map.get('rel');
+					const rel_values = rel ? rel.get_static_value().split(' ') : [];
+					const expected_values = ['noreferrer'];
+
+					expected_values.forEach(expected_value => {
+						if (!rel || rel && rel_values.indexOf(expected_value) < 0) {
+							component.warn(this, {
+								code: `security-anchor-rel-${expected_value}`,
+								message: `Security: Anchor with "target=_blank" should have rel attribute containing the value "${expected_value}"`
+							});
+						}
+					});
+				}
+			}
 
 			if (href_attribute) {
 				const href_value = href_attribute.get_static_value();
@@ -729,7 +753,7 @@ export default class Element extends Node {
 		if (this.name === 'figure') {
 			const children = this.children.filter(node => {
 				if (node.type === 'Comment') return false;
-				if (node.type === 'Text') return /\S/.test(node.data);
+				if (node.type === 'Text') return regex_non_whitespace_character.test(node.data);
 				return true;
 			});
 
@@ -861,7 +885,7 @@ export default class Element extends Node {
 				if (this.name !== 'video') {
 					return component.error(binding, compiler_errors.invalid_binding_element_with('<video>', name));
 				}
-			} else if (dimensions.test(name)) {
+			} else if (regex_dimensions.test(name)) {
 				if (this.name === 'svg' && (name === 'offsetWidth' || name === 'offsetHeight')) {
 					return component.error(binding, compiler_errors.invalid_binding_on(binding.name, `<svg>. Use '${name.replace('offset', 'client')}' instead`));
 				} else if (is_svg(this.name)) {
@@ -988,7 +1012,7 @@ export default class Element extends Node {
 			if (attribute && !attribute.is_true) {
 				attribute.chunks.forEach((chunk, index) => {
 					if (chunk.type === 'Text') {
-						let data = chunk.data.replace(/[\s\n\t]+/g, ' ');
+						let data = chunk.data.replace(regex_any_repeated_whitespaces, ' ');
 						if (index === 0) {
 							data = data.trimLeft();
 						} else if (index === attribute.chunks.length - 1) {
@@ -1002,12 +1026,14 @@ export default class Element extends Node {
 	}
 }
 
+const regex_starts_with_vovel = /^[aeiou]/;
+
 function should_have_attribute(
 	node,
 	attributes: string[],
 	name = node.name
 ) {
-	const article = /^[aeiou]/.test(attributes[0]) ? 'an' : 'a';
+	const article = regex_starts_with_vovel.test(attributes[0]) ? 'an' : 'a';
 	const sequence = attributes.length > 1 ?
 		attributes.slice(0, -1).join(', ') + ` or ${attributes[attributes.length - 1]}` :
 		attributes[0];
@@ -1015,10 +1041,12 @@ function should_have_attribute(
 	node.component.warn(node, compiler_warnings.a11y_missing_attribute(name, article, sequence));
 }
 
+const regex_minus_sign = /-/;
+
 function within_custom_element(parent: INode) {
 	while (parent) {
 		if (parent.type === 'InlineComponent') return false;
-		if (parent.type === 'Element' && /-/.test(parent.name)) return true;
+		if (parent.type === 'Element' && regex_minus_sign.test(parent.name)) return true;
 		parent = parent.parent;
 	}
 	return false;
diff --git a/src/compiler/compile/nodes/EventHandler.ts b/src/compiler/compile/nodes/EventHandler.ts
index 1bac53b6af..4b426580b3 100644
--- a/src/compiler/compile/nodes/EventHandler.ts
+++ b/src/compiler/compile/nodes/EventHandler.ts
@@ -6,6 +6,8 @@ import { Identifier } from 'estree';
 import TemplateScope from './shared/TemplateScope';
 import { TemplateNode } from '../../interfaces';
 
+const regex_contains_term_function_expression = /FunctionExpression/;
+
 export default class EventHandler extends Node {
 	type: 'EventHandler';
 	name: string;
@@ -25,7 +27,7 @@ export default class EventHandler extends Node {
 			this.expression = new Expression(component, this, template_scope, info.expression);
 			this.uses_context = this.expression.uses_context;
 
-			if (/FunctionExpression/.test(info.expression.type) && info.expression.params.length === 0) {
+			if (regex_contains_term_function_expression.test(info.expression.type) && info.expression.params.length === 0) {
 				// TODO make this detection more accurate — if `event.preventDefault` isn't called, and
 				// `event` is passed to another function, we can make it passive
 				this.can_make_passive = true;
@@ -55,7 +57,7 @@ export default class EventHandler extends Node {
 		}
 		const node = this.expression.node;
 
-		if (/FunctionExpression/.test(node.type)) {
+		if (regex_contains_term_function_expression.test(node.type)) {
 			return false;
 		}
 
diff --git a/src/compiler/compile/nodes/Head.ts b/src/compiler/compile/nodes/Head.ts
index fb000e0d5b..1ebe0c053a 100644
--- a/src/compiler/compile/nodes/Head.ts
+++ b/src/compiler/compile/nodes/Head.ts
@@ -5,6 +5,7 @@ import Component from '../Component';
 import TemplateScope from './shared/TemplateScope';
 import { TemplateNode } from '../../interfaces';
 import compiler_errors from '../compiler_errors';
+import { regex_non_whitespace_character } from '../../utils/patterns';
 
 export default class Head extends Node {
 	type: 'Head';
@@ -20,7 +21,7 @@ export default class Head extends Node {
 		}
 
 		this.children = map_children(component, parent, scope, info.children.filter(child => {
-			return (child.type !== 'Text' || /\S/.test(child.data));
+			return (child.type !== 'Text' || regex_non_whitespace_character.test(child.data));
 		}));
 
 		if (this.children.length > 0) {
diff --git a/src/compiler/compile/nodes/InlineComponent.ts b/src/compiler/compile/nodes/InlineComponent.ts
index 8871c5f306..26cfeb7ef9 100644
--- a/src/compiler/compile/nodes/InlineComponent.ts
+++ b/src/compiler/compile/nodes/InlineComponent.ts
@@ -10,6 +10,7 @@ import TemplateScope from './shared/TemplateScope';
 import { INode } from './interfaces';
 import { TemplateNode } from '../../interfaces';
 import compiler_errors from '../compiler_errors';
+import { regex_only_whitespaces } from '../../utils/patterns';
 
 export default class InlineComponent extends Node {
 	type: 'InlineComponent';
@@ -73,10 +74,10 @@ export default class InlineComponent extends Node {
 
 				case 'Transition':
 					return component.error(node, compiler_errors.invalid_transition);
-				
+
 				case 'StyleDirective':
 					return component.error(node, compiler_errors.invalid_component_style_directive);
-	
+
 				default:
 					throw new Error(`Not implemented: ${node.type}`);
 			}
@@ -165,7 +166,7 @@ export default class InlineComponent extends Node {
 }
 
 function not_whitespace_text(node) {
-	return !(node.type === 'Text' && /^\s+$/.test(node.data));
+	return !(node.type === 'Text' && regex_only_whitespaces.test(node.data));
 }
 
 function get_namespace(parent: Node, explicit_namespace: string) {
diff --git a/src/compiler/compile/nodes/StyleDirective.ts b/src/compiler/compile/nodes/StyleDirective.ts
index ea340cf2dc..01af8cc62e 100644
--- a/src/compiler/compile/nodes/StyleDirective.ts
+++ b/src/compiler/compile/nodes/StyleDirective.ts
@@ -1,20 +1,42 @@
 import { TemplateNode } from '../../interfaces';
+import list from '../../utils/list';
+import compiler_errors from '../compiler_errors';
 import Component from '../Component';
 import { nodes_to_template_literal } from '../utils/nodes_to_template_literal';
 import Expression from './shared/Expression';
 import Node from './shared/Node';
 import TemplateScope from './shared/TemplateScope';
 
+const valid_modifiers = new Set(['important']);
+
 export default class StyleDirective extends Node {
 	type: 'StyleDirective';
 	name: string;
+	modifiers: Set<string>;
 	expression: Expression;
 	should_cache: boolean;
 
-	constructor(component: Component, parent: Node, scope: TemplateScope, info: TemplateNode) {
+	constructor(
+		component: Component,
+		parent: Node,
+		scope: TemplateScope,
+		info: TemplateNode
+	) {
 		super(component, parent, scope, info);
 
 		this.name = info.name;
+		this.modifiers = new Set(info.modifiers);
+
+		for (const modifier of this.modifiers) {
+			if (!valid_modifiers.has(modifier)) {
+				component.error(
+					this,
+					compiler_errors.invalid_style_directive_modifier(
+						list([...valid_modifiers])
+					)
+				);
+			}
+		}
 
 		// Convert the value array to an expression so it's easier to handle
 		// the StyleDirective going forward.
@@ -34,6 +56,9 @@ export default class StyleDirective extends Node {
 			this.expression = new Expression(component, this, scope, raw_expression);
 			this.should_cache = raw_expression.expressions.length > 0;
 		}
+	}
 
+	get important() {
+		return this.modifiers.has('important');
 	}
 }
diff --git a/src/compiler/compile/nodes/Text.ts b/src/compiler/compile/nodes/Text.ts
index 347beb9c23..ac6cd9b828 100644
--- a/src/compiler/compile/nodes/Text.ts
+++ b/src/compiler/compile/nodes/Text.ts
@@ -3,6 +3,7 @@ import Component from '../Component';
 import TemplateScope from './shared/TemplateScope';
 import { INode } from './interfaces';
 import { TemplateNode } from '../../interfaces';
+import { regex_non_whitespace_character } from '../../utils/patterns';
 
 // Whitespace inside one of these elements will not result in
 // a whitespace node being created in any circumstances. (This
@@ -16,6 +17,8 @@ const elements_without_text = new Set([
 	'video'
 ]);
 
+const regex_ends_with_svg = /svg$/;
+
 export default class Text extends Node {
 	type: 'Text';
 	data: string;
@@ -28,7 +31,7 @@ export default class Text extends Node {
 	}
 
 	should_skip() {
-		if (/\S/.test(this.data)) return false;
+		if (regex_non_whitespace_character.test(this.data)) return false;
 
 		const parent_element = this.find_nearest(/(?:Element|InlineComponent|SlotTemplate|Head)/);
 		if (!parent_element) return false;
@@ -37,7 +40,7 @@ export default class Text extends Node {
 		if (parent_element.type === 'InlineComponent') return parent_element.children.length === 1 && this === parent_element.children[0];
 
 		// svg namespace exclusions
-		if (/svg$/.test(parent_element.namespace)) {
+		if (regex_ends_with_svg.test(parent_element.namespace)) {
 			if (this.prev && this.prev.type === 'Element' && this.prev.name === 'tspan') return false;
 		}
 
diff --git a/src/compiler/compile/nodes/shared/AbstractBlock.ts b/src/compiler/compile/nodes/shared/AbstractBlock.ts
index 04917f5a6b..91af3fc0f7 100644
--- a/src/compiler/compile/nodes/shared/AbstractBlock.ts
+++ b/src/compiler/compile/nodes/shared/AbstractBlock.ts
@@ -4,6 +4,8 @@ import Node from './Node';
 import { INode } from '../interfaces';
 import compiler_warnings from '../../compiler_warnings';
 
+const regex_non_whitespace_characters = /[^ \r\n\f\v\t]/;
+
 export default class AbstractBlock extends Node {
 	block: Block;
 	children: INode[];
@@ -17,7 +19,7 @@ export default class AbstractBlock extends Node {
 
 		const child = this.children[0];
 
-		if (!child || (child.type === 'Text' && !/[^ \r\n\f\v\t]/.test(child.data))) {
+		if (!child || (child.type === 'Text' && !regex_non_whitespace_characters.test(child.data))) {
 			this.component.warn(this, compiler_warnings.empty_block);
 		}
 	}
diff --git a/src/compiler/compile/nodes/shared/Expression.ts b/src/compiler/compile/nodes/shared/Expression.ts
index 0603c15589..d726b811a1 100644
--- a/src/compiler/compile/nodes/shared/Expression.ts
+++ b/src/compiler/compile/nodes/shared/Expression.ts
@@ -21,6 +21,8 @@ import compiler_errors from '../../compiler_errors';
 
 type Owner = INode;
 
+const regex_contains_term_function_expression = /FunctionExpression/;
+
 export default class Expression {
 	type: 'Expression' = 'Expression';
 	component: Component;
@@ -72,7 +74,7 @@ export default class Expression {
 					scope = map.get(node);
 				}
 
-				if (!function_expression && /FunctionExpression/.test(node.type)) {
+				if (!function_expression && regex_contains_term_function_expression.test(node.type)) {
 					function_expression = node;
 				}
 
@@ -126,6 +128,7 @@ export default class Expression {
 						deep = node.left.type === 'MemberExpression';
 						names = extract_names(deep ? get_object(node.left) : node.left);
 					} else if (node.type === 'UpdateExpression') {
+                        deep = node.argument.type === 'MemberExpression';
 						names = extract_names(get_object(node.argument));
 					}
 				}
@@ -147,7 +150,26 @@ export default class Expression {
 							component.add_reference(node, name);
 
 							const variable = component.var_lookup.get(name);
-							if (variable) variable[deep ? 'mutated' : 'reassigned'] = true;
+
+							if (variable) {
+								variable[deep ? 'mutated' : 'reassigned'] = true;
+							}
+
+							const declaration: any = scope.find_owner(name)?.declarations.get(name);
+
+							if (declaration) {
+								if (declaration.kind === 'const' && !deep) {
+									component.error(node, {
+										code: 'assignment-to-const',
+										message: 'You are assigning to a const'
+									});
+								}
+							} else if (variable && variable.writable === false && !deep) {
+								component.error(node, {
+									code: 'assignment-to-const',
+									message: 'You are assigning to a const'
+								});
+							}
 						}
 					});
 				}
diff --git a/src/compiler/compile/render_dom/Block.ts b/src/compiler/compile/render_dom/Block.ts
index 34c4774804..164e938674 100644
--- a/src/compiler/compile/render_dom/Block.ts
+++ b/src/compiler/compile/render_dom/Block.ts
@@ -3,6 +3,7 @@ import Wrapper from './wrappers/shared/Wrapper';
 import { b, x } from 'code-red';
 import { Node, Identifier, ArrayPattern } from 'estree';
 import { is_head } from './wrappers/shared/is_head';
+import { regex_double_quotes } from '../../utils/patterns';
 
 export interface Bindings {
 	object: Identifier;
@@ -415,7 +416,7 @@ export default class Block {
 						block: ${block},
 						id: ${this.name || 'create_fragment'}.name,
 						type: "${this.type}",
-						source: "${this.comment ? this.comment.replace(/"/g, '\\"') : ''}",
+						source: "${this.comment ? this.comment.replace(regex_double_quotes, '\\"') : ''}",
 						ctx: #ctx
 					});
 					return ${block};`
diff --git a/src/compiler/compile/render_dom/Renderer.ts b/src/compiler/compile/render_dom/Renderer.ts
index 179fc0c956..c00ef95586 100644
--- a/src/compiler/compile/render_dom/Renderer.ts
+++ b/src/compiler/compile/render_dom/Renderer.ts
@@ -168,7 +168,7 @@ export default class Renderer {
 		return member;
 	}
 
-	invalidate(name: string, value?, main_execution_context: boolean = false) {
+	invalidate(name: string, value?: unknown, main_execution_context: boolean = false) {
 		return renderer_invalidate(this, name, value, main_execution_context);
 	}
 
diff --git a/src/compiler/compile/render_dom/index.ts b/src/compiler/compile/render_dom/index.ts
index b06c5b577c..44155f8464 100644
--- a/src/compiler/compile/render_dom/index.ts
+++ b/src/compiler/compile/render_dom/index.ts
@@ -12,6 +12,7 @@ import { RawSourceMap, DecodedSourceMap } from '@ampproject/remapping/dist/types
 import { flatten } from '../../utils/flatten';
 import check_enable_sourcemap from '../utils/check_enable_sourcemap';
 import { push_array } from '../../utils/push_array';
+import { regex_backslashes } from '../../utils/patterns';
 
 export default function dom(
 	component: Component,
@@ -82,7 +83,7 @@ export default function dom(
 	}
 
 	const uses_slots = component.var_lookup.has('$$slots');
-	let compute_slots;
+	let compute_slots: Node[] | undefined;
 	if (uses_slots) {
 		compute_slots = b`
 			const $$slots = @compute_slots(#slots);
@@ -395,7 +396,7 @@ export default function dom(
 
 	if (has_definition) {
 		const reactive_declarations: (Node | Node[]) = [];
-		const fixed_reactive_declarations = []; // not really 'reactive' but whatever
+		const fixed_reactive_declarations: Node[] = []; // not really 'reactive' but whatever
 
 		component.reactive_declarations.forEach(d => {
 			const dependencies = Array.from(d.dependencies);
@@ -440,7 +441,7 @@ export default function dom(
 			return b`let ${$name};`;
 		});
 
-		let unknown_props_check;
+		let unknown_props_check: Node[] | undefined;
 		if (component.compile_options.dev && !(uses_props || uses_rest)) {
 			unknown_props_check = b`
 				const writable_props = [${writable_props.map(prop => x`'${prop.export_name}'`)}];
@@ -530,7 +531,7 @@ export default function dom(
 				constructor(options) {
 					super();
 
-					${css.code && b`this.shadowRoot.innerHTML = \`<style>${css.code.replace(/\\/g, '\\\\')}${css_sourcemap_enabled && options.dev ? `\n/*# sourceMappingURL=${css.map.toUrl()} */` : ''}</style>\`;`}
+					${css.code && b`this.shadowRoot.innerHTML = \`<style>${css.code.replace(regex_backslashes, '\\\\')}${css_sourcemap_enabled && options.dev ? `\n/*# sourceMappingURL=${css.map.toUrl()} */` : ''}</style>\`;`}
 
 					@init(this, { target: this.shadowRoot, props: ${init_props}, customElement: true }, ${definition}, ${has_create_fragment ? 'create_fragment' : 'null'}, ${not_equal}, ${prop_indexes}, null, ${dirty});
 
diff --git a/src/compiler/compile/render_dom/invalidate.ts b/src/compiler/compile/render_dom/invalidate.ts
index 7eeb34a894..ffc5b6b42e 100644
--- a/src/compiler/compile/render_dom/invalidate.ts
+++ b/src/compiler/compile/render_dom/invalidate.ts
@@ -80,7 +80,7 @@ export function invalidate(renderer: Renderer, scope: Scope, node: Node, names:
 	return invalidate;
 }
 
-export function renderer_invalidate(renderer: Renderer, name: string, value?, main_execution_context: boolean = false) {
+export function renderer_invalidate(renderer: Renderer, name: string, value?: unknown, main_execution_context: boolean = false) {
 	const variable = renderer.component.var_lookup.get(name);
 
 	if (variable && (variable.subscribable && (variable.reassigned || variable.export_name))) {
diff --git a/src/compiler/compile/render_dom/wrappers/EachBlock.ts b/src/compiler/compile/render_dom/wrappers/EachBlock.ts
index d4648954ca..0c49c38028 100644
--- a/src/compiler/compile/render_dom/wrappers/EachBlock.ts
+++ b/src/compiler/compile/render_dom/wrappers/EachBlock.ts
@@ -582,7 +582,7 @@ export default class EachBlockWrapper extends Wrapper {
 
 			const start = this.block.has_update_method ? 0 : '#old_length';
 
-			let remove_old_blocks;
+			let remove_old_blocks: Node[];
 
 			if (this.block.has_outros) {
 				const out = block.get_unique_name('out');
diff --git a/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts b/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts
index 21a44ab92a..81a1898331 100644
--- a/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts
+++ b/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts
@@ -10,6 +10,7 @@ import handle_select_value_binding from './handle_select_value_binding';
 import { Identifier, Node } from 'estree';
 import { namespaces } from '../../../../utils/namespaces';
 import { boolean_attributes } from '../../../../../shared/boolean_attributes';
+import { regex_double_quotes } from '../../../../utils/patterns';
 
 const non_textlike_input_types = new Set([
 	'button',
@@ -42,9 +43,12 @@ export class BaseAttributeWrapper {
 		}
 	}
 
-	render(_block: Block) {}
+	render(_block: Block) { }
 }
 
+const regex_minus_sign = /-/;
+const regex_invalid_variable_identifier_characters = /[^a-zA-Z_$]/g;
+
 export default class AttributeWrapper extends BaseAttributeWrapper {
 	node: Attribute;
 	parent: ElementWrapper;
@@ -115,7 +119,7 @@ export default class AttributeWrapper extends BaseAttributeWrapper {
 		// xlink is a special case... we could maybe extend this to generic
 		// namespaced attributes but I'm not sure that's applicable in
 		// HTML5?
-		const method = /-/.test(element.node.name)
+		const method = regex_minus_sign.test(element.node.name)
 			? '@set_custom_element_data'
 			: name.slice(0, 6) === 'xlink:'
 				? '@xlink_attr'
@@ -126,7 +130,7 @@ export default class AttributeWrapper extends BaseAttributeWrapper {
 		const dependencies = this.get_dependencies();
 		const value = this.get_value(block);
 
-		let updater;
+		let updater: Node[];
 		const init = this.get_init(block, value);
 
 		if (is_legacy_input_type) {
@@ -196,7 +200,7 @@ export default class AttributeWrapper extends BaseAttributeWrapper {
 
 	get_init(block: Block, value) {
 		this.last = this.should_cache && block.get_unique_name(
-			`${this.parent.var.name}_${this.name.replace(/[^a-zA-Z_$]/g, '_')}_value`
+			`${this.parent.var.name}_${this.name.replace(regex_invalid_variable_identifier_characters, '_')}_value`
 		);
 
 		if (this.should_cache) block.add_variable(this.last);
@@ -254,7 +258,7 @@ export default class AttributeWrapper extends BaseAttributeWrapper {
 		return metadata;
 	}
 
-	get_value(block) {
+	get_value(block: Block) {
 		if (this.node.is_true) {
 			if (this.metadata && boolean_attributes.has(this.metadata.property_name.toLowerCase())) {
 				return x`true`;
@@ -283,7 +287,7 @@ export default class AttributeWrapper extends BaseAttributeWrapper {
 		return value;
 	}
 
-	get_class_name_text(block) {
+	get_class_name_text(block: Block) {
 		const scoped_css = this.node.chunks.some((chunk: Text) => chunk.synthetic);
 		const rendered = this.render_chunks(block);
 
@@ -313,7 +317,7 @@ export default class AttributeWrapper extends BaseAttributeWrapper {
 
 		return `="${value.map(chunk => {
 			return chunk.type === 'Text'
-				? chunk.data.replace(/"/g, '\\"')
+				? chunk.data.replace(regex_double_quotes, '\\"')
 				: `\${${chunk.manipulate()}}`;
 		}).join('')}"`;
 	}
@@ -381,13 +385,14 @@ function should_cache(attribute: AttributeWrapper) {
 	return attribute.is_src || attribute.node.should_cache();
 }
 
+const regex_contains_checked_or_group = /checked|group/;
+
 function is_indirectly_bound_value(attribute: AttributeWrapper) {
 	const element = attribute.parent;
 	return attribute.name === 'value' &&
 		(element.node.name === 'option' || // TODO check it's actually bound
 			(element.node.name === 'input' &&
 				element.node.bindings.some(
-					(binding) =>
-						/checked|group/.test(binding.name)
+					(binding) => regex_contains_checked_or_group.test(binding.name)
 				)));
 }
diff --git a/src/compiler/compile/render_dom/wrappers/Element/Binding.ts b/src/compiler/compile/render_dom/wrappers/Element/Binding.ts
index bc218a510b..9e2ec85f0f 100644
--- a/src/compiler/compile/render_dom/wrappers/Element/Binding.ts
+++ b/src/compiler/compile/render_dom/wrappers/Element/Binding.ts
@@ -299,8 +299,8 @@ function get_binding_group(renderer: Renderer, value: Binding, block: Block) {
 
 	for (const dep of contextual_dependencies) {
 		const context = block.bindings.get(dep);
-		let key;
-		let name;
+		let key: string;
+		let name: string;
 		if (context) {
 			key = context.object.name;
 			name = context.property.name;
@@ -364,7 +364,7 @@ function get_event_handler(
 	const contextual_dependencies = new Set<string>(binding.node.expression.contextual_dependencies);
 
 	const context = block.bindings.get(name);
-	let set_store;
+	let set_store: Node[] | undefined;
 
 	if (context) {
 		const { object, property, store, snippet } = context;
diff --git a/src/compiler/compile/render_dom/wrappers/Element/EventHandler.ts b/src/compiler/compile/render_dom/wrappers/Element/EventHandler.ts
index fc65a9aa5e..b0ed4a73d6 100644
--- a/src/compiler/compile/render_dom/wrappers/Element/EventHandler.ts
+++ b/src/compiler/compile/render_dom/wrappers/Element/EventHandler.ts
@@ -26,7 +26,7 @@ export default class EventHandlerWrapper {
 		}
 	}
 
-	get_snippet(block) {
+	get_snippet(block: Block) {
 		const snippet = this.node.expression ? this.node.expression.manipulate(block) : block.renderer.reference(this.node.handler_name);
 
 		if (this.node.reassigned) {
diff --git a/src/compiler/compile/render_dom/wrappers/Element/StyleAttribute.ts b/src/compiler/compile/render_dom/wrappers/Element/StyleAttribute.ts
index ac7f66b6ac..4481b6b98f 100644
--- a/src/compiler/compile/render_dom/wrappers/Element/StyleAttribute.ts
+++ b/src/compiler/compile/render_dom/wrappers/Element/StyleAttribute.ts
@@ -69,6 +69,8 @@ export default class StyleAttributeWrapper extends AttributeWrapper {
 	}
 }
 
+const regex_style_prop_key = /^\s*([\w-]+):\s*/;
+
 function optimize_style(value: Array<Text | Expression>) {
 	const props: StyleProp[] = [];
 	let chunks = value.slice();
@@ -78,7 +80,7 @@ function optimize_style(value: Array<Text | Expression>) {
 
 		if (chunk.type !== 'Text') return null;
 
-		const key_match = /^\s*([\w-]+):\s*/.exec(chunk.data);
+		const key_match = regex_style_prop_key.exec(chunk.data);
 		if (!key_match) return null;
 
 		const key = key_match[1];
@@ -106,6 +108,9 @@ function optimize_style(value: Array<Text | Expression>) {
 	return props;
 }
 
+const regex_important_flag = /\s*!important\s*$/;
+const regex_semicolon_or_whitespace = /[;\s]/;
+
 function get_style_value(chunks: Array<Text | Expression>) {
 	const value: Array<Text | Expression> = [];
 
@@ -151,7 +156,7 @@ function get_style_value(chunks: Array<Text | Expression>) {
 				} as Text);
 			}
 
-			while (/[;\s]/.test(chunk.data[c])) c += 1;
+			while (regex_semicolon_or_whitespace.test(chunk.data[c])) c += 1;
 			const remaining_data = chunk.data.slice(c);
 
 			if (remaining_data) {
@@ -172,9 +177,9 @@ function get_style_value(chunks: Array<Text | Expression>) {
 	let important = false;
 
 	const last_chunk = value[value.length - 1];
-	if (last_chunk && last_chunk.type === 'Text' && /\s*!important\s*$/.test(last_chunk.data)) {
+	if (last_chunk && last_chunk.type === 'Text' && regex_important_flag.test(last_chunk.data)) {
 		important = true;
-		last_chunk.data = last_chunk.data.replace(/\s*!important\s*$/, '');
+		last_chunk.data = last_chunk.data.replace(regex_important_flag, '');
 		if (!last_chunk.data) value.pop();
 	}
 
diff --git a/src/compiler/compile/render_dom/wrappers/Element/fix_attribute_casing.ts b/src/compiler/compile/render_dom/wrappers/Element/fix_attribute_casing.ts
index 7044d5d7b3..0ff7c27e4b 100644
--- a/src/compiler/compile/render_dom/wrappers/Element/fix_attribute_casing.ts
+++ b/src/compiler/compile/render_dom/wrappers/Element/fix_attribute_casing.ts
@@ -6,7 +6,7 @@ svg_attributes.forEach(name => {
 	svg_attribute_lookup.set(name.toLowerCase(), name);
 });
 
-export default function fix_attribute_casing(name) {
+export default function fix_attribute_casing(name: string) {
 	name = name.toLowerCase();
 	return svg_attribute_lookup.get(name) || name;
 }
diff --git a/src/compiler/compile/render_dom/wrappers/Element/index.ts b/src/compiler/compile/render_dom/wrappers/Element/index.ts
index 4f0b49729c..8d0429879e 100644
--- a/src/compiler/compile/render_dom/wrappers/Element/index.ts
+++ b/src/compiler/compile/render_dom/wrappers/Element/index.ts
@@ -12,14 +12,14 @@ import { namespaces } from '../../../../utils/namespaces';
 import AttributeWrapper from './Attribute';
 import StyleAttributeWrapper from './StyleAttribute';
 import SpreadAttributeWrapper from './SpreadAttribute';
-import { dimensions, start_newline } from '../../../../utils/patterns';
+import { regex_dimensions, regex_starts_with_newline, regex_backslashes } from '../../../../utils/patterns';
 import Binding from './Binding';
 import add_to_set from '../../../utils/add_to_set';
 import { add_event_handler } from '../shared/add_event_handlers';
 import { add_action } from '../shared/add_actions';
 import bind_this from '../shared/bind_this';
 import { is_head } from '../shared/is_head';
-import { Identifier, ExpressionStatement, CallExpression } from 'estree';
+import { Identifier, ExpressionStatement, CallExpression, Node } from 'estree';
 import EventHandler from './EventHandler';
 import { extract_names } from 'periscopic';
 import Action from '../../../nodes/Action';
@@ -34,12 +34,16 @@ interface BindingGroup {
 	bindings: Binding[];
 }
 
+const regex_contains_radio_or_checkbox_or_file = /radio|checkbox|file/;
+const regex_contains_radio_or_checkbox_or_range_or_file = /radio|checkbox|range|file/;
+
 const events = [
 	{
 		event_names: ['input'],
 		filter: (node: Element, _name: string) =>
 			node.name === 'textarea' ||
-			node.name === 'input' && !/radio|checkbox|range|file/.test(node.get_static_attribute_value('type') as string)
+			node.name === 'input' &&
+			!regex_contains_radio_or_checkbox_or_range_or_file.test(node.get_static_attribute_value('type') as string)
 	},
 	{
 		event_names: ['input'],
@@ -51,7 +55,8 @@ const events = [
 		event_names: ['change'],
 		filter: (node: Element, _name: string) =>
 			node.name === 'select' ||
-			node.name === 'input' && /radio|checkbox|file/.test(node.get_static_attribute_value('type') as string)
+			node.name === 'input' &&
+			regex_contains_radio_or_checkbox_or_file.test(node.get_static_attribute_value('type') as string)
 	},
 	{
 		event_names: ['change', 'input'],
@@ -62,7 +67,7 @@ const events = [
 	{
 		event_names: ['elementresize'],
 		filter: (_node: Element, name: string) =>
-			dimensions.test(name)
+			regex_dimensions.test(name)
 	},
 
 	// media events
@@ -136,6 +141,8 @@ const events = [
 ];
 
 const CHILD_DYNAMIC_ELEMENT_BLOCK = 'child_dynamic_element';
+const regex_invalid_variable_identifier_characters = /[^a-zA-Z0-9_$]/g;
+const regex_minus_signs = /-/g;
 
 export default class ElementWrapper extends Wrapper {
 	node: Element;
@@ -182,7 +189,7 @@ export default class ElementWrapper extends Wrapper {
 
 		this.var = {
 			type: 'Identifier',
-			name: node.name.replace(/[^a-zA-Z0-9_$]/g, '_')
+			name: node.name.replace(regex_invalid_variable_identifier_characters, '_')
 		};
 
 		this.void = is_void(node.name);
@@ -527,7 +534,7 @@ export default class ElementWrapper extends Wrapper {
 			.filter((attr) => !(attr instanceof SpreadAttributeWrapper) && !attr.property_name)
 			.map((attr) => p`${(attr as StyleAttributeWrapper | AttributeWrapper).name}: true`);
 
-		let reference;
+		let reference: string | ReturnType<typeof x>;
 		if (this.node.tag_expr.node.type === 'Literal') {
 			if (this.node.namespace) {
 				reference = `"${this.node.tag_expr.node.value}"`;
@@ -547,7 +554,7 @@ export default class ElementWrapper extends Wrapper {
 		}
 	}
 
-	add_directives_in_order (block: Block) {
+	add_directives_in_order(block: Block) {
 		type OrderedAttribute = EventHandler | BindingGroup | Binding | Action;
 
 		const binding_groups = events
@@ -561,7 +568,7 @@ export default class ElementWrapper extends Wrapper {
 
 		const this_binding = this.bindings.find(b => b.node.name === 'this');
 
-		function getOrder (item: OrderedAttribute) {
+		function getOrder(item: OrderedAttribute) {
 			if (item instanceof EventHandler) {
 				return item.node.start;
 			} else if (item instanceof Binding) {
@@ -627,7 +634,7 @@ export default class ElementWrapper extends Wrapper {
 		// media bindings — awkward special case. The native timeupdate events
 		// fire too infrequently, so we need to take matters into our
 		// own hands
-		let animation_frame;
+		let animation_frame: Identifier | undefined;
 		if (binding_group.events[0] === 'timeupdate') {
 			animation_frame = block.get_unique_name(`${this.var.name}_animationframe`);
 			block.add_variable(animation_frame);
@@ -867,9 +874,7 @@ export default class ElementWrapper extends Wrapper {
 		}
 	}
 
-	add_transitions(
-		block: Block
-	) {
+	add_transitions(block: Block) {
 		const { intro, outro } = this.node;
 		if (!intro && !outro) return;
 
@@ -926,7 +931,7 @@ export default class ElementWrapper extends Wrapper {
 
 				const fn = this.renderer.reference(intro.name);
 
-				let intro_block;
+				let intro_block: Node[];
 
 				if (outro) {
 					intro_block = b`
@@ -1025,7 +1030,7 @@ export default class ElementWrapper extends Wrapper {
 			${outro && b`@add_transform(${this.var}, ${rect});`}
 		`);
 
-		let params;
+		let params: Node | ReturnType<typeof x>;
 		if (this.node.animation.expression) {
 			params = this.node.animation.expression.manipulate(block);
 
@@ -1053,8 +1058,8 @@ export default class ElementWrapper extends Wrapper {
 		const has_spread = this.node.attributes.some(attr => attr.is_spread);
 		this.node.classes.forEach(class_directive => {
 			const { expression, name } = class_directive;
-			let snippet;
-			let dependencies;
+			let snippet: Node | string;
+			let dependencies: Set<string>;
 			if (expression) {
 				snippet = expression.manipulate(block);
 				dependencies = expression.dependencies;
@@ -1095,16 +1100,16 @@ export default class ElementWrapper extends Wrapper {
 	add_styles(block: Block) {
 		const has_spread = this.node.attributes.some(attr => attr.is_spread);
 		this.node.styles.forEach((style_directive) => {
-			const { name, expression, should_cache } = style_directive;
+			const { name, expression, should_cache, important } = style_directive;
 
 			const snippet = expression.manipulate(block);
-			let cached_snippet;
+			let cached_snippet: Identifier | undefined;
 			if (should_cache) {
-				cached_snippet = block.get_unique_name(`style_${name.replace(/-/g, '_')}`);
+				cached_snippet = block.get_unique_name(`style_${name.replace(regex_minus_signs, '_')}`);
 				block.add_variable(cached_snippet, snippet);
 			}
 
-			const updater = b`@set_style(${this.var}, "${name}", ${should_cache ? cached_snippet : snippet}, false)`;
+			const updater = b`@set_style(${this.var}, "${name}", ${should_cache ? cached_snippet : snippet}, ${important ? 1 : null})`;
 
 			block.chunks.hydrate.push(updater);
 
@@ -1129,7 +1134,7 @@ export default class ElementWrapper extends Wrapper {
 		});
 	}
 
-	add_manual_style_scoping(block) {
+	add_manual_style_scoping(block: Block) {
 		if (this.node.needs_manual_style_scoping) {
 			const updater = b`@toggle_class(${this.var}, "${this.node.component.stylesheet.id}", true);`;
 			block.chunks.hydrate.push(updater);
@@ -1138,10 +1143,13 @@ export default class ElementWrapper extends Wrapper {
 	}
 }
 
+const regex_backticks = /`/g;
+const regex_dollar_signs = /\$/g;
+
 function to_html(wrappers: Array<ElementWrapper | TextWrapper | MustacheTagWrapper | RawMustacheTagWrapper>, block: Block, literal: any, state: any, can_use_raw_text?: boolean) {
 	wrappers.forEach(wrapper => {
 		if (wrapper instanceof TextWrapper) {
-			// Don't add the <pre>/<textare> newline logic here because pre/textarea.innerHTML
+			// Don't add the <pre>/<textarea> newline logic here because pre/textarea.innerHTML
 			// would keep the leading newline, too, only someParent.innerHTML = '..<pre/textarea>..' won't
 
 			if ((wrapper as TextWrapper).use_space()) state.quasi.value.raw += ' ';
@@ -1155,9 +1163,9 @@ function to_html(wrappers: Array<ElementWrapper | TextWrapper | MustacheTagWrapp
 			);
 
 			state.quasi.value.raw += (raw ? wrapper.data : escape_html(wrapper.data))
-				.replace(/\\/g, '\\\\')
-				.replace(/`/g, '\\`')
-				.replace(/\$/g, '\\$');
+				.replace(regex_backslashes, '\\\\')
+				.replace(regex_backticks, '\\`')
+				.replace(regex_dollar_signs, '\\$');
 		} else if (wrapper instanceof MustacheTagWrapper || wrapper instanceof RawMustacheTagWrapper) {
 			literal.quasis.push(state.quasi);
 			literal.expressions.push(wrapper.node.expression.manipulate(block));
@@ -1192,7 +1200,7 @@ function to_html(wrappers: Array<ElementWrapper | TextWrapper | MustacheTagWrapp
 					// Two or more leading newlines are required to restore the leading newline immediately after `<pre>`.
 					// see https://html.spec.whatwg.org/multipage/grouping-content.html#the-pre-element
 					const first = wrapper.fragment.nodes[0];
-					if (first && first.node.type === 'Text' && start_newline.test(first.node.data)) {
+					if (first && first.node.type === 'Text' && regex_starts_with_newline.test(first.node.data)) {
 						state.quasi.value.raw += '\n';
 					}
 				}
@@ -1204,7 +1212,7 @@ function to_html(wrappers: Array<ElementWrapper | TextWrapper | MustacheTagWrapp
 						// Two or more leading newlines are required to restore the leading newline immediately after `<textarea>`.
 						// see https://html.spec.whatwg.org/multipage/syntax.html#element-restrictions
 						const first = value_attribute.node.chunks[0];
-						if (first && first.type === 'Text' && start_newline.test(first.data)) {
+						if (first && first.type === 'Text' && regex_starts_with_newline.test(first.data)) {
 							state.quasi.value.raw += '\n';
 						}
 						to_html_for_attr_value(value_attribute, block, literal, state);
diff --git a/src/compiler/compile/render_dom/wrappers/Fragment.ts b/src/compiler/compile/render_dom/wrappers/Fragment.ts
index 87ce775ca9..e2eb519393 100644
--- a/src/compiler/compile/render_dom/wrappers/Fragment.ts
+++ b/src/compiler/compile/render_dom/wrappers/Fragment.ts
@@ -21,6 +21,7 @@ import Block from '../Block';
 import { trim_start, trim_end } from '../../../utils/trim';
 import { link } from '../../../utils/link';
 import { Identifier } from 'estree';
+import { regex_starts_with_whitespace } from '../../../utils/patterns';
 
 const wrappers = {
 	AwaitBlock,
@@ -64,7 +65,7 @@ export default class FragmentWrapper {
 		this.nodes = [];
 
 		let last_child: Wrapper;
-		let window_wrapper;
+		let window_wrapper: Window | undefined;
 
 		let i = nodes.length;
 		while (i--) {
@@ -92,7 +93,7 @@ export default class FragmentWrapper {
 				// *unless* there is no whitespace between this node and its next sibling
 				if (this.nodes.length === 0) {
 					const should_trim = (
-						next_sibling ? (next_sibling.node.type === 'Text' && /^\s/.test(next_sibling.node.data) && trimmable_at(child, next_sibling)) : !child.has_ancestor('EachBlock')
+						next_sibling ? (next_sibling.node.type === 'Text' && regex_starts_with_whitespace.test(next_sibling.node.data) && trimmable_at(child, next_sibling)) : !child.has_ancestor('EachBlock')
 					);
 
 					if (should_trim && !child.keep_space()) {
diff --git a/src/compiler/compile/render_dom/wrappers/Head.ts b/src/compiler/compile/render_dom/wrappers/Head.ts
index 3869994ae4..7915604f98 100644
--- a/src/compiler/compile/render_dom/wrappers/Head.ts
+++ b/src/compiler/compile/render_dom/wrappers/Head.ts
@@ -33,7 +33,7 @@ export default class HeadWrapper extends Wrapper {
 	}
 
 	render(block: Block, _parent_node: Identifier, _parent_nodes: Identifier) {
-		let nodes;
+		let nodes: Identifier;
 		if (this.renderer.options.hydratable && this.fragment.nodes.length) {
 			nodes = block.get_unique_name('head_nodes');
 			block.chunks.claim.push(b`const ${nodes} = @head_selector('${this.node.id}', @_document.head);`);
diff --git a/src/compiler/compile/render_dom/wrappers/IfBlock.ts b/src/compiler/compile/render_dom/wrappers/IfBlock.ts
index d74ce270bf..9c4798c69c 100644
--- a/src/compiler/compile/render_dom/wrappers/IfBlock.ts
+++ b/src/compiler/compile/render_dom/wrappers/IfBlock.ts
@@ -13,6 +13,8 @@ import { Identifier, Node } from 'estree';
 import { push_array } from '../../../utils/push_array';
 import { add_const_tags, add_const_tags_context } from './shared/add_const_tags';
 
+type DetachingOrNull = 'detaching' | null;
+
 function is_else_if(node: ElseBlock) {
 	return (
 		node && node.children.length === 1 && node.children[0].type === 'IfBlock'
@@ -213,7 +215,7 @@ export default class IfBlockWrapper extends Wrapper {
 
 		const vars = { name, anchor, if_exists_condition, has_else, has_transitions };
 
-		const detaching = parent_node && !is_head(parent_node) ? null : 'detaching';
+		const detaching: DetachingOrNull = parent_node && !is_head(parent_node) ? null : 'detaching';
 
 		if (this.node.else) {
 			this.branches.forEach(branch => {
@@ -275,9 +277,9 @@ export default class IfBlockWrapper extends Wrapper {
 		block: Block,
 		parent_node: Identifier,
 		_parent_nodes: Identifier,
-		dynamic,
+		dynamic: boolean,
 		{ name, anchor, has_else, if_exists_condition, has_transitions },
-		detaching
+		detaching: DetachingOrNull
 	) {
 		const select_block_type = this.renderer.component.get_unique_name('select_block_type');
 		const current_block_type = block.get_unique_name('current_block_type');
@@ -414,9 +416,9 @@ export default class IfBlockWrapper extends Wrapper {
 		block: Block,
 		parent_node: Identifier,
 		_parent_nodes: Identifier,
-		dynamic,
+		dynamic: boolean,
 		{ name, anchor, has_else, has_transitions, if_exists_condition },
-		detaching
+		detaching: DetachingOrNull
 	) {
 		const select_block_type = this.renderer.component.get_unique_name('select_block_type');
 		const current_block_type_index = block.get_unique_name('current_block_type_index');
@@ -428,8 +430,8 @@ export default class IfBlockWrapper extends Wrapper {
 		const if_ctx = select_block_ctx ? x`${select_block_ctx}(#ctx, ${current_block_type_index})` : x`#ctx`;
 
 		const if_current_block_type_index = has_else
-			? nodes => nodes
-			: nodes => b`if (~${current_block_type_index}) { ${nodes} }`;
+			? (nodes: Node[]) => nodes
+			: (nodes: Node[]) => b`if (~${current_block_type_index}) { ${nodes} }`;
 
 		block.add_variable(current_block_type_index);
 		block.add_variable(name);
@@ -593,9 +595,9 @@ export default class IfBlockWrapper extends Wrapper {
 		block: Block,
 		parent_node: Identifier,
 		_parent_nodes: Identifier,
-		dynamic,
+		dynamic: boolean,
 		{ name, anchor, if_exists_condition, has_transitions },
-		detaching
+		detaching: DetachingOrNull
 	) {
 		const branch = this.branches[0];
 		const if_ctx = branch.get_ctx_name ? x`${branch.get_ctx_name}(#ctx)` : x`#ctx`;
diff --git a/src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts b/src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts
index 37aaf2e7b2..bca01fdb4c 100644
--- a/src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts
+++ b/src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts
@@ -24,6 +24,8 @@ import { namespaces } from '../../../../utils/namespaces';
 
 type SlotDefinition = { block: Block; scope: TemplateScope; get_context?: Node; get_changes?: Node };
 
+const regex_invalid_variable_identifier_characters = /[^a-zA-Z_$]/g;
+
 export default class InlineComponentWrapper extends Wrapper {
 	var: Identifier;
 	slots: Map<string, SlotDefinition> = new Map();
@@ -137,7 +139,7 @@ export default class InlineComponentWrapper extends Wrapper {
 			child.render(block, null, x`#nodes` as Identifier);
 		});
 
-		let props;
+		let props: Identifier | undefined;
 		const name_changes = block.get_unique_name(`${name.name}_changes`);
 
 		const uses_spread = !!this.node.attributes.find(a => a.is_spread);
@@ -232,7 +234,7 @@ export default class InlineComponentWrapper extends Wrapper {
 						: null;
 					const unchanged = dependencies.size === 0;
 
-					let change_object;
+					let change_object: Node | ReturnType<typeof x>;
 					if (attr.is_spread) {
 						const value = attr.expression.manipulate(block);
 						initial_props.push(value);
@@ -596,7 +598,7 @@ export default class InlineComponentWrapper extends Wrapper {
 		this.node.css_custom_properties.forEach((attr) => {
 			const dependencies = attr.get_dependencies();
 			const should_cache = attr.should_cache();
-			const last = should_cache &&	block.get_unique_name(`${attr.name.replace(/[^a-zA-Z_$]/g, '_')}_last`);
+			const last = should_cache &&	block.get_unique_name(`${attr.name.replace(regex_invalid_variable_identifier_characters, '_')}_last`);
 			if (should_cache) block.add_variable(last);
 			const value = attr.get_value(block);
 			const init = should_cache ? x`${last} = ${value}` : value;
diff --git a/src/compiler/compile/render_dom/wrappers/RawMustacheTag.ts b/src/compiler/compile/render_dom/wrappers/RawMustacheTag.ts
index 7810d8f099..8dc8460e1d 100644
--- a/src/compiler/compile/render_dom/wrappers/RawMustacheTag.ts
+++ b/src/compiler/compile/render_dom/wrappers/RawMustacheTag.ts
@@ -8,7 +8,7 @@ import Element from '../../nodes/Element';
 import MustacheTag from '../../nodes/MustacheTag';
 import RawMustacheTag from '../../nodes/RawMustacheTag';
 import { is_head } from './shared/is_head';
-import { Identifier } from 'estree';
+import { Identifier, Node } from 'estree';
 
 export default class RawMustacheTagWrapper extends Tag {
 	var: Identifier = { type: 'Identifier', name: 'raw' };
@@ -30,7 +30,7 @@ export default class RawMustacheTagWrapper extends Tag {
 		const can_use_innerhtml = !in_head && parent_node && !this.prev && !this.next;
 
 		if (can_use_innerhtml) {
-			const insert = content => b`${parent_node}.innerHTML = ${content};`[0];
+			const insert = (content: Node) => b`${parent_node}.innerHTML = ${content};`[0];
 
 			const { init } = this.rename_this_method(
 				block,
diff --git a/src/compiler/compile/render_dom/wrappers/Slot.ts b/src/compiler/compile/render_dom/wrappers/Slot.ts
index 5a778ba5fb..0a589e3394 100644
--- a/src/compiler/compile/render_dom/wrappers/Slot.ts
+++ b/src/compiler/compile/render_dom/wrappers/Slot.ts
@@ -9,7 +9,7 @@ import add_to_set from '../../utils/add_to_set';
 import get_slot_data from '../../utils/get_slot_data';
 import { is_reserved_keyword } from '../../utils/reserved_keywords';
 import is_dynamic from './shared/is_dynamic';
-import { Identifier, ObjectExpression } from 'estree';
+import { Identifier, ObjectExpression, Node } from 'estree';
 import create_debugging_comment from './shared/create_debugging_comment';
 
 export default class SlotWrapper extends Wrapper {
@@ -75,9 +75,9 @@ export default class SlotWrapper extends Wrapper {
 			block = this.slot_block;
 		}
 
-		let get_slot_changes_fn;
-		let get_slot_spread_changes_fn;
-		let get_slot_context_fn;
+		let get_slot_changes_fn: Identifier | 'null';
+		let get_slot_spread_changes_fn: Identifier | undefined;
+		let get_slot_context_fn: Identifier | 'null';
 
 		if (this.node.values.size > 0) {
 			get_slot_changes_fn = renderer.component.get_unique_name(`get_${sanitize(slot_name)}_slot_changes`);
@@ -176,7 +176,7 @@ export default class SlotWrapper extends Wrapper {
 		].filter(Boolean);
 		const all_dirty_condition = all_dirty_conditions.length ? all_dirty_conditions.reduce((condition1, condition2) => x`${condition1} || ${condition2}`) : null;
 
-		let slot_update;
+		let slot_update: Node[];
 		if (all_dirty_condition) {
 			const dirty = x`${all_dirty_condition} ? @get_all_dirty_from_scope(${renderer.reference('$$scope')}) : @get_slot_changes(${slot_definition}, ${renderer.reference('$$scope')}, #dirty, ${get_slot_changes_fn})`;
 
diff --git a/src/compiler/compile/render_dom/wrappers/Text.ts b/src/compiler/compile/render_dom/wrappers/Text.ts
index 2a342b5678..7d02735d9a 100644
--- a/src/compiler/compile/render_dom/wrappers/Text.ts
+++ b/src/compiler/compile/render_dom/wrappers/Text.ts
@@ -5,6 +5,8 @@ import Wrapper from './shared/Wrapper';
 import { x } from 'code-red';
 import { Identifier } from 'estree';
 
+const regex_non_whitespace_characters = /[\S\u00A0]/;
+
 export default class TextWrapper extends Wrapper {
 	node: Text;
 	data: string;
@@ -27,7 +29,7 @@ export default class TextWrapper extends Wrapper {
 
 	use_space() {
 		if (this.renderer.component.component_options.preserveWhitespace) return false;
-		if (/[\S\u00A0]/.test(this.data)) return false;
+		if (regex_non_whitespace_characters.test(this.data)) return false;
 
 		return !this.node.within_pre();
 	}
diff --git a/src/compiler/compile/render_dom/wrappers/Window.ts b/src/compiler/compile/render_dom/wrappers/Window.ts
index 3c55680446..c98af18268 100644
--- a/src/compiler/compile/render_dom/wrappers/Window.ts
+++ b/src/compiler/compile/render_dom/wrappers/Window.ts
@@ -45,7 +45,7 @@ export default class WindowWrapper extends Wrapper {
 		const { renderer } = this;
 		const { component } = renderer;
 
-		const events = {};
+		const events: Record<string, Array<{ name: string; value: string }>> = {};
 		const bindings: Record<string, string> = {};
 
 		add_actions(block, '@_window', this.node.actions);
diff --git a/src/compiler/compile/render_dom/wrappers/shared/add_actions.ts b/src/compiler/compile/render_dom/wrappers/shared/add_actions.ts
index 6429f18928..734cfea972 100644
--- a/src/compiler/compile/render_dom/wrappers/shared/add_actions.ts
+++ b/src/compiler/compile/render_dom/wrappers/shared/add_actions.ts
@@ -1,7 +1,7 @@
 import { b, x } from 'code-red';
 import Block from '../../Block';
 import Action from '../../../nodes/Action';
-import { Expression } from 'estree';
+import { Expression, Node } from 'estree';
 import is_contextual from '../../../nodes/shared/is_contextual';
 
 export default function add_actions(
@@ -12,10 +12,12 @@ export default function add_actions(
 	actions.forEach(action => add_action(block, target, action));
 }
 
+const regex_invalid_variable_identifier_characters = /[^a-zA-Z0-9_$]/g;
+
 export function add_action(block: Block, target: string | Expression, action: Action) {
 	const { expression, template_scope } = action;
-	let snippet;
-	let dependencies;
+	let snippet: Node | undefined;
+	let dependencies: string[] | undefined;
 
 	if (expression) {
 		snippet = expression.manipulate(block);
@@ -23,7 +25,7 @@ export function add_action(block: Block, target: string | Expression, action: Ac
 	}
 
 	const id = block.get_unique_name(
-		`${action.name.replace(/[^a-zA-Z0-9_$]/g, '_')}_action`
+		`${action.name.replace(regex_invalid_variable_identifier_characters, '_')}_action`
 	);
 
 	block.add_variable(id);
diff --git a/src/compiler/compile/render_dom/wrappers/shared/create_debugging_comment.ts b/src/compiler/compile/render_dom/wrappers/shared/create_debugging_comment.ts
index 8e9f7fab37..9e989dc49c 100644
--- a/src/compiler/compile/render_dom/wrappers/shared/create_debugging_comment.ts
+++ b/src/compiler/compile/render_dom/wrappers/shared/create_debugging_comment.ts
@@ -1,5 +1,7 @@
 import Component from '../../../Component';
 import { INode } from '../../../nodes/interfaces';
+import { regex_whitespace_characters } from '../../../../utils/patterns';
+
 
 export default function create_debugging_comment(
 	node: INode,
@@ -13,7 +15,7 @@ export default function create_debugging_comment(
 		while (source[c - 1] === '{') c -= 1;
 	}
 
-	let d;
+	let d: number;
 
 	if (node.type === 'InlineComponent' || node.type === 'Element' || node.type === 'SlotTemplate') {
 		if (node.children.length) {
@@ -36,5 +38,5 @@ export default function create_debugging_comment(
 	const start = locate(c);
 	const loc = `(${start.line}:${start.column})`;
 
-	return `${loc} ${source.slice(c, d)}`.replace(/\s/g, ' ');
+	return `${loc} ${source.slice(c, d)}`.replace(regex_whitespace_characters, ' ');
 }
diff --git a/src/compiler/compile/render_dom/wrappers/shared/get_slot_definition.ts b/src/compiler/compile/render_dom/wrappers/shared/get_slot_definition.ts
index 2279c7c845..2114096988 100644
--- a/src/compiler/compile/render_dom/wrappers/shared/get_slot_definition.ts
+++ b/src/compiler/compile/render_dom/wrappers/shared/get_slot_definition.ts
@@ -2,7 +2,7 @@ import Let from '../../../nodes/Let';
 import { x, p } from 'code-red';
 import Block from '../../Block';
 import TemplateScope from '../../../nodes/shared/TemplateScope';
-import { BinaryExpression } from 'estree';
+import { BinaryExpression, Identifier } from 'estree';
 
 export function get_slot_definition(block: Block, scope: TemplateScope, lets: Let[]) {
 	if (lets.length === 0) return { block, scope };
@@ -21,7 +21,7 @@ export function get_slot_definition(block: Block, scope: TemplateScope, lets: Le
 	const value_map = new Map();
 
 	lets.forEach(l => {
-		let value;
+		let value: Identifier;
 		if (l.names.length > 1) {
 			// more than one, probably destructuring
 			const unique_name = block.get_unique_name(l.names.join('_')).name;
@@ -86,7 +86,7 @@ export function get_slot_definition(block: Block, scope: TemplateScope, lets: Le
 					elements[g] = grouped[g]
 						? grouped[g]
 							.map(({ name, n }) => x`${name} ? ${1 << n} : 0`)
-							.reduce((lhs, rhs) => x`${lhs} | ${rhs}`)
+							.reduce((lhs: ReturnType<typeof x>, rhs: ReturnType<typeof x>) => x`${lhs} | ${rhs}`)
 						: x`0`;
 				}
 
diff --git a/src/compiler/compile/render_dom/wrappers/shared/is_head.ts b/src/compiler/compile/render_dom/wrappers/shared/is_head.ts
index 36bf571aad..da34274d5b 100644
--- a/src/compiler/compile/render_dom/wrappers/shared/is_head.ts
+++ b/src/compiler/compile/render_dom/wrappers/shared/is_head.ts
@@ -1,3 +1,5 @@
-export function is_head(node) {
-	return node && node.type === 'MemberExpression' && node.object.name === '@_document' && node.property.name === 'head';
+import { Node } from 'estree';
+
+export function is_head(node: Node) {
+	return node && node.type === 'MemberExpression' && node.object['name'] === '@_document' && node.property['name'] === 'head';
 }
diff --git a/src/compiler/compile/render_ssr/handlers/Element.ts b/src/compiler/compile/render_ssr/handlers/Element.ts
index 2af0343b2a..f1dd86dd2b 100644
--- a/src/compiler/compile/render_ssr/handlers/Element.ts
+++ b/src/compiler/compile/render_ssr/handlers/Element.ts
@@ -8,7 +8,7 @@ import Expression from '../../nodes/shared/Expression';
 import remove_whitespace_children from './utils/remove_whitespace_children';
 import fix_attribute_casing from '../../render_dom/wrappers/Element/fix_attribute_casing';
 import { namespaces } from '../../../utils/namespaces';
-import { start_newline } from '../../../utils/patterns';
+import { regex_starts_with_newline } from '../../../utils/patterns';
 import { Node, Expression as ESExpression } from 'estree';
 
 export default function (node: Element, renderer: Renderer, options: RenderOptions) {
@@ -44,7 +44,10 @@ export default function (node: Element, renderer: Renderer, options: RenderOptio
 		class_expression_list.reduce((lhs, rhs) => x`${lhs} + ' ' + ${rhs}`);
 
 	const style_expression_list = node.styles.map(style_directive => {
-		const { name, expression: { node: expression } } = style_directive;
+		let { name, important, expression: { node: expression } } = style_directive;
+		if (important) {
+			expression = x`${expression} + ' !important'`;
+		}
 		return p`"${name}": ${expression}`;
 	});
 
@@ -173,7 +176,7 @@ export default function (node: Element, renderer: Renderer, options: RenderOptio
 				const value_attribute = node.attributes.find(({ name }) => name === 'value');
 				if (value_attribute) {
 					const first = value_attribute.chunks[0];
-					if (first && first.type === 'Text' && start_newline.test(first.data)) {
+					if (first && first.type === 'Text' && regex_starts_with_newline.test(first.data)) {
 						renderer.add_string('\n');
 					}
 				}
@@ -188,7 +191,7 @@ export default function (node: Element, renderer: Renderer, options: RenderOptio
 			// see https://html.spec.whatwg.org/multipage/grouping-content.html#the-pre-element
 			// see https://html.spec.whatwg.org/multipage/syntax.html#element-restrictions
 			const first = children[0];
-			if (first && first.type === 'Text' && start_newline.test(first.data)) {
+			if (first && first.type === 'Text' && regex_starts_with_newline.test(first.data)) {
 				renderer.add_string('\n');
 			}
 		}
diff --git a/src/compiler/compile/render_ssr/handlers/Head.ts b/src/compiler/compile/render_ssr/handlers/Head.ts
index f4bb3fa118..95648e1aca 100644
--- a/src/compiler/compile/render_ssr/handlers/Head.ts
+++ b/src/compiler/compile/render_ssr/handlers/Head.ts
@@ -1,6 +1,7 @@
 import Renderer, { RenderOptions } from '../Renderer';
 import Head from '../../nodes/Head';
 import { x } from 'code-red';
+import { Node } from 'estree';
 
 export default function(node: Head, renderer: Renderer, options: RenderOptions) {
 	const head_options = {
@@ -11,6 +12,12 @@ export default function(node: Head, renderer: Renderer, options: RenderOptions)
 	renderer.push();
 	renderer.render(node.children, head_options);
 	const result = renderer.pop();
+	let expression: Node = result;
+	if (options.hydratable) {
+		const start_comment = `HEAD_${node.id}_START`;
+		const end_comment = `HEAD_${node.id}_END`;
+		expression = x`'<!-- ${start_comment} -->' + ${expression} + '<!-- ${end_comment} -->'`;
+	}
 
-	renderer.add_expression(x`$$result.head += '<!-- HEAD_${node.id}_START -->' + ${result} + '<!-- HEAD_${node.id}_END -->', ""`);
+	renderer.add_expression(x`$$result.head += ${expression}, ""`);
 }
diff --git a/src/compiler/compile/render_ssr/handlers/shared/get_attribute_value.ts b/src/compiler/compile/render_ssr/handlers/shared/get_attribute_value.ts
index 20d4eddbc5..f431ea01db 100644
--- a/src/compiler/compile/render_ssr/handlers/shared/get_attribute_value.ts
+++ b/src/compiler/compile/render_ssr/handlers/shared/get_attribute_value.ts
@@ -4,6 +4,7 @@ import Text from '../../../nodes/Text';
 import { x } from 'code-red';
 import Expression from '../../../nodes/shared/Expression';
 import { Expression as ESTreeExpression } from 'estree';
+import { regex_double_quotes } from '../../../../utils/patterns';
 
 export function get_class_attribute_value(attribute: Attribute): ESTreeExpression {
 	// handle special case — `class={possiblyUndefined}` with scoped CSS
@@ -21,7 +22,7 @@ export function get_attribute_value(attribute: Attribute): ESTreeExpression {
 	return attribute.chunks
 		.map((chunk) => {
 			return chunk.type === 'Text'
-				? string_literal(chunk.data.replace(/"/g, '&quot;')) as ESTreeExpression
+				? string_literal(chunk.data.replace(regex_double_quotes, '&quot;')) as ESTreeExpression
 				: x`@escape(${chunk.node}, true)`;
 		})
 		.reduce((lhs, rhs) => x`${lhs} + ${rhs}`);
diff --git a/src/compiler/compile/render_ssr/handlers/utils/remove_whitespace_children.ts b/src/compiler/compile/render_ssr/handlers/utils/remove_whitespace_children.ts
index 7733c89cb8..10ccaefa92 100644
--- a/src/compiler/compile/render_ssr/handlers/utils/remove_whitespace_children.ts
+++ b/src/compiler/compile/render_ssr/handlers/utils/remove_whitespace_children.ts
@@ -1,6 +1,7 @@
 import { INode } from '../../../nodes/interfaces';
 import { trim_end, trim_start } from '../../../../utils/trim';
 import { link } from '../../../../utils/link';
+import { regex_starts_with_whitespace } from '../../../../utils/patterns';
 
 // similar logic from `compile/render_dom/wrappers/Fragment`
 // We want to remove trailing whitespace inside an element/component/block,
@@ -22,7 +23,7 @@ export default function remove_whitespace_children(children: INode[], next?: INo
 			if (nodes.length === 0) {
 				const should_trim = next
 					? next.type === 'Text' &&
-					  /^\s/.test(next.data) &&
+					regex_starts_with_whitespace.test(next.data) &&
 					  trimmable_at(child, next)
 					: !child.has_ancestor('EachBlock');
 
diff --git a/src/compiler/compile/utils/get_name_from_filename.ts b/src/compiler/compile/utils/get_name_from_filename.ts
index b05605b5ee..7c0f805b76 100644
--- a/src/compiler/compile/utils/get_name_from_filename.ts
+++ b/src/compiler/compile/utils/get_name_from_filename.ts
@@ -1,3 +1,10 @@
+import { regex_starts_with_underscore, regex_ends_with_underscore } from '../../utils/patterns';
+
+const regex_percentage_characters = /%/g;
+const regex_file_ending = /\.[^.]+$/;
+const regex_repeated_invalid_variable_identifier_characters = /[^a-zA-Z_$0-9]+/g;
+const regex_starts_with_digit = /^(\d)/;
+
 export default function get_name_from_filename(filename: string) {
 	if (!filename) return null;
 
@@ -12,12 +19,12 @@ export default function get_name_from_filename(filename: string) {
 	}
 
 	const base = parts.pop()
-		.replace(/%/g, 'u')
-		.replace(/\.[^.]+$/, '')
-		.replace(/[^a-zA-Z_$0-9]+/g, '_')
-		.replace(/^_/, '')
-		.replace(/_$/, '')
-		.replace(/^(\d)/, '_$1');
+		.replace(regex_percentage_characters, 'u')
+		.replace(regex_file_ending, '')
+		.replace(regex_repeated_invalid_variable_identifier_characters, '_')
+		.replace(regex_starts_with_underscore, '')
+		.replace(regex_ends_with_underscore, '')
+		.replace(regex_starts_with_digit, '_$1');
 
 	if (!base) {
 		throw new Error(`Could not derive component name from file ${filename}`);
diff --git a/src/compiler/compile/utils/hash.ts b/src/compiler/compile/utils/hash.ts
index c0ea2b3d88..d5b5a20609 100644
--- a/src/compiler/compile/utils/hash.ts
+++ b/src/compiler/compile/utils/hash.ts
@@ -1,6 +1,9 @@
 // https://github.com/darkskyapp/string-hash/blob/master/index.js
+
+const regex_return_characters = /\r/g;
+
 export default function hash(str: string): string {
-	str = str.replace(/\r/g, '');
+	str = str.replace(regex_return_characters, '');
 	let hash = 5381;
 	let i = str.length;
 
diff --git a/src/compiler/compile/utils/stringify.ts b/src/compiler/compile/utils/stringify.ts
index aa1c42c512..84073c6469 100644
--- a/src/compiler/compile/utils/stringify.ts
+++ b/src/compiler/compile/utils/stringify.ts
@@ -19,10 +19,14 @@ const escaped = {
 	'>': '&gt;'
 };
 
+const regex_html_characters_to_escape = /["'&<>]/g;
+
 export function escape_html(html) {
-	return String(html).replace(/["'&<>]/g, match => escaped[match]);
+	return String(html).replace(regex_html_characters_to_escape, match => escaped[match]);
 }
 
+const regex_template_characters_to_escape = /(\${|`|\\)/g;
+
 export function escape_template(str) {
-	return str.replace(/(\${|`|\\)/g, '\\$1');
+	return str.replace(regex_template_characters_to_escape, '\\$1');
 }
diff --git a/src/compiler/parse/errors.ts b/src/compiler/parse/errors.ts
index 63bd5b0919..26f03c0cb1 100644
--- a/src/compiler/parse/errors.ts
+++ b/src/compiler/parse/errors.ts
@@ -107,6 +107,14 @@ export default {
 		code: `invalid-${slug}-placement`,
 		message: `<${name}> tags cannot be inside elements or blocks`
 	}),
+	invalid_logic_block_placement: (location: string, name: string) => ({
+		code: 'invalid-logic-block-placement',
+		message: `{#${name}} logic block cannot be ${location}`
+	}),
+	invalid_tag_placement: (location: string, name: string) => ({
+		code: 'invalid-tag-placement',
+		message: `{@${name}} tag cannot be ${location}`
+	}),
 	invalid_ref_directive: (name: string) => ({
 		code: 'invalid-ref-directive',
 		message: `The ref directive is no longer supported — use \`bind:this={${name}}\` instead`
diff --git a/src/compiler/parse/index.ts b/src/compiler/parse/index.ts
index ce873c7d84..8de6563c8b 100644
--- a/src/compiler/parse/index.ts
+++ b/src/compiler/parse/index.ts
@@ -1,6 +1,6 @@
 import { isIdentifierStart, isIdentifierChar } from 'acorn';
 import fragment from './state/fragment';
-import { whitespace } from '../utils/patterns';
+import { regex_whitespace } from '../utils/patterns';
 import { reserved } from '../utils/names';
 import full_char_code_at from '../utils/full_char_code_at';
 import { TemplateNode, Ast, ParserOptions, Fragment, Style, Script } from '../interfaces';
@@ -15,6 +15,8 @@ interface LastAutoClosedTag {
 	depth: number;
 }
 
+const regex_position_indicator = / \(\d+:\d+\)$/;
+
 export class Parser {
 	readonly template: string;
 	readonly filename?: string;
@@ -76,10 +78,10 @@ export class Parser {
 
 		if (this.html.children.length) {
 			let start = this.html.children[0].start;
-			while (whitespace.test(template[start])) start += 1;
+			while (regex_whitespace.test(template[start])) start += 1;
 
 			let end = this.html.children[this.html.children.length - 1].end;
-			while (whitespace.test(template[end - 1])) end -= 1;
+			while (regex_whitespace.test(template[end - 1])) end -= 1;
 
 			this.html.start = start;
 			this.html.end = end;
@@ -95,7 +97,7 @@ export class Parser {
 	acorn_error(err: any) {
 		this.error({
 			code: 'parse-error',
-			message: err.message.replace(/ \(\d+:\d+\)$/, '')
+			message: err.message.replace(regex_position_indicator, '')
 		}, err.pos);
 	}
 
@@ -140,7 +142,7 @@ export class Parser {
 	allow_whitespace() {
 		while (
 			this.index < this.template.length &&
-			whitespace.test(this.template[this.index])
+			regex_whitespace.test(this.template[this.index])
 		) {
 			this.index++;
 		}
@@ -202,7 +204,7 @@ export class Parser {
 	}
 
 	require_whitespace() {
-		if (!whitespace.test(this.template[this.index])) {
+		if (!regex_whitespace.test(this.template[this.index])) {
 			this.error({
 				code: 'missing-whitespace',
 				message: 'Expected whitespace'
diff --git a/src/compiler/parse/read/context.ts b/src/compiler/parse/read/context.ts
index 1e97baf8a7..134d11a6ad 100644
--- a/src/compiler/parse/read/context.ts
+++ b/src/compiler/parse/read/context.ts
@@ -10,6 +10,7 @@ import {
 import { parse_expression_at } from '../acorn';
 import { Pattern } from 'estree';
 import parser_errors from '../errors';
+import { regex_not_newline_characters } from '../../utils/patterns';
 
 export default function read_context(
 	parser: Parser
@@ -65,7 +66,7 @@ export default function read_context(
 		// so we offset it by removing 1 character in the `space_with_newline`
 		// to achieve that, we remove the 1st space encountered,
 		// so it will not affect the `column` of the node
-		let space_with_newline = parser.template.slice(0, start).replace(/[^\n]/g, ' ');
+		let space_with_newline = parser.template.slice(0, start).replace(regex_not_newline_characters, ' ');
 		const first_space = space_with_newline.indexOf(' ');
 		space_with_newline = space_with_newline.slice(0, first_space) + space_with_newline.slice(first_space + 1);
 
diff --git a/src/compiler/parse/read/expression.ts b/src/compiler/parse/read/expression.ts
index 5464a950ce..935574440f 100644
--- a/src/compiler/parse/read/expression.ts
+++ b/src/compiler/parse/read/expression.ts
@@ -1,7 +1,7 @@
 import { parse_expression_at } from '../acorn';
 import { Parser } from '../index';
 import { Node } from 'estree';
-import { whitespace } from '../../utils/patterns';
+import { regex_whitespace } from '../../utils/patterns';
 import parser_errors from '../errors';
 
 export default function read_expression(parser: Parser): Node {
@@ -20,7 +20,7 @@ export default function read_expression(parser: Parser): Node {
 
 			if (char === ')') {
 				num_parens -= 1;
-			} else if (!whitespace.test(char)) {
+			} else if (!regex_whitespace.test(char)) {
 				parser.error(parser_errors.unexpected_token(')'), index);
 			}
 
diff --git a/src/compiler/parse/read/script.ts b/src/compiler/parse/read/script.ts
index c9ac4ac344..02506ab3d5 100644
--- a/src/compiler/parse/read/script.ts
+++ b/src/compiler/parse/read/script.ts
@@ -3,6 +3,9 @@ import { Parser } from '../index';
 import { Script } from '../../interfaces';
 import { Node, Program } from 'estree';
 import parser_errors from '../errors';
+import { regex_not_newline_characters } from '../../utils/patterns';
+
+const regex_closing_script_tag = /<\/script\s*>/;
 
 function get_context(parser: Parser, attributes: any[], start: number): string {
 	const context = attributes.find(attribute => attribute.name === 'context');
@@ -23,13 +26,13 @@ function get_context(parser: Parser, attributes: any[], start: number): string {
 
 export default function read_script(parser: Parser, start: number, attributes: Node[]): Script {
 	const script_start = parser.index;
-	const data = parser.read_until(/<\/script\s*>/, parser_errors.unclosed_script);
+	const data = parser.read_until(regex_closing_script_tag, parser_errors.unclosed_script);
 	if (parser.index >= parser.template.length) {
 		parser.error(parser_errors.unclosed_script);
 	}
 
-	const source = parser.template.slice(0, script_start).replace(/[^\n]/g, ' ') + data;
-	parser.read(/<\/script\s*>/);
+	const source = parser.template.slice(0, script_start).replace(regex_not_newline_characters, ' ') + data;
+	parser.read(regex_closing_script_tag);
 
 	let ast: Program;
 
diff --git a/src/compiler/parse/read/style.ts b/src/compiler/parse/read/style.ts
index c4788466ec..560d377cec 100644
--- a/src/compiler/parse/read/style.ts
+++ b/src/compiler/parse/read/style.ts
@@ -1,15 +1,17 @@
-import parse from 'css-tree/lib/parser/index.js';
+// @ts-ignore
+import parse from 'css-tree/parser';
 import { walk } from 'estree-walker';
 import { Parser } from '../index';
 import { Node } from 'estree';
 import { Style } from '../../interfaces';
 import parser_errors from '../errors';
 
+const regex_closing_style_tag = /<\/style\s*>/;
+
 export default function read_style(parser: Parser, start: number, attributes: Node[]): Style {
 	const content_start = parser.index;
 
-	const tag_close_pattern = /<\/style\s*>/;
-	const styles = parser.read_until(tag_close_pattern, parser_errors.unclosed_style);
+	const styles = parser.read_until(regex_closing_style_tag, parser_errors.unclosed_style);
 
 	if (parser.index >= parser.template.length) {
 		parser.error(parser_errors.unclosed_style);
@@ -19,7 +21,7 @@ export default function read_style(parser: Parser, start: number, attributes: No
 
 	// discard styles when css is disabled
 	if (parser.css_mode === 'none') {
-		parser.read(tag_close_pattern);
+		parser.read(regex_closing_style_tag);
 		return null;
 	}
 
@@ -74,7 +76,8 @@ export default function read_style(parser: Parser, start: number, attributes: No
 		}
 	});
 
-	parser.read(tag_close_pattern);
+	parser.read(regex_closing_style_tag);
+  
 	const end = parser.index;
 
 	return {
diff --git a/src/compiler/parse/state/mustache.ts b/src/compiler/parse/state/mustache.ts
index da9016a9df..c3b58afe2a 100644
--- a/src/compiler/parse/state/mustache.ts
+++ b/src/compiler/parse/state/mustache.ts
@@ -1,7 +1,7 @@
 import read_context from '../read/context';
 import read_expression from '../read/expression';
 import { closing_tag_omitted } from '../utils/html';
-import { whitespace } from '../../utils/patterns';
+import { regex_whitespace } from '../../utils/patterns';
 import { trim_start, trim_end } from '../../utils/trim';
 import { to_string } from '../utils/node';
 import { Parser } from '../index';
@@ -33,6 +33,8 @@ function trim_whitespace(block: TemplateNode, trim_before: boolean, trim_after:
 	}
 }
 
+const regex_whitespace_with_closing_curly_brace = /\s*}/;
+
 export default function mustache(parser: Parser) {
 	const start = parser.index;
 	parser.index += 1;
@@ -87,8 +89,8 @@ export default function mustache(parser: Parser) {
 		// strip leading/trailing whitespace as necessary
 		const char_before = parser.template[block.start - 1];
 		const char_after = parser.template[parser.index];
-		const trim_before = !char_before || whitespace.test(char_before);
-		const trim_after = !char_after || whitespace.test(char_after);
+		const trim_before = !char_before || regex_whitespace.test(char_before);
+		const trim_after = !char_after || regex_whitespace.test(char_after);
 
 		trim_whitespace(block, trim_before, trim_after);
 
@@ -106,8 +108,8 @@ export default function mustache(parser: Parser) {
 			const block = parser.current();
 			if (block.type !== 'IfBlock') {
 				parser.error(
-					parser.stack.some(block => block.type === 'IfBlock') 
-						? parser_errors.invalid_elseif_placement_unclosed_block(to_string(block)) 
+					parser.stack.some(block => block.type === 'IfBlock')
+						? parser_errors.invalid_elseif_placement_unclosed_block(to_string(block))
 						: parser_errors.invalid_elseif_placement_outside_if
 				);
 			}
@@ -141,8 +143,8 @@ export default function mustache(parser: Parser) {
 			const block = parser.current();
 			if (block.type !== 'IfBlock' && block.type !== 'EachBlock') {
 				parser.error(
-					parser.stack.some(block => block.type === 'IfBlock' || block.type === 'EachBlock') 
-						? parser_errors.invalid_else_placement_unclosed_block(to_string(block)) 
+					parser.stack.some(block => block.type === 'IfBlock' || block.type === 'EachBlock')
+						? parser_errors.invalid_else_placement_unclosed_block(to_string(block))
 						: parser_errors.invalid_else_placement_outside_if
 				);
 			}
@@ -167,15 +169,15 @@ export default function mustache(parser: Parser) {
 			if (block.type !== 'PendingBlock') {
 				parser.error(
 					parser.stack.some(block => block.type === 'PendingBlock')
-						? parser_errors.invalid_then_placement_unclosed_block(to_string(block)) 
-						: parser_errors.invalid_then_placement_without_await 
+						? parser_errors.invalid_then_placement_unclosed_block(to_string(block))
+						: parser_errors.invalid_then_placement_without_await
 				);
 			}
 		} else {
 			if (block.type !== 'ThenBlock' && block.type !== 'PendingBlock') {
 				parser.error(parser.stack.some(block => block.type === 'ThenBlock' || block.type === 'PendingBlock')
-						? parser_errors.invalid_catch_placement_unclosed_block(to_string(block)) 
-						: parser_errors.invalid_catch_placement_without_await 
+					? parser_errors.invalid_catch_placement_unclosed_block(to_string(block))
+					: parser_errors.invalid_catch_placement_without_await
 				);
 			}
 		}
@@ -290,7 +292,7 @@ export default function mustache(parser: Parser) {
 
 		const await_block_shorthand = type === 'AwaitBlock' && parser.eat('then');
 		if (await_block_shorthand) {
-			if (parser.match_regex(/\s*}/)) {
+			if (parser.match_regex(regex_whitespace_with_closing_curly_brace)) {
 				parser.allow_whitespace();
 			} else {
 				parser.require_whitespace();
@@ -301,7 +303,7 @@ export default function mustache(parser: Parser) {
 
 		const await_block_catch_shorthand = !await_block_shorthand && type === 'AwaitBlock' && parser.eat('catch');
 		if (await_block_catch_shorthand) {
-			if (parser.match_regex(/\s*}/)) {
+			if (parser.match_regex(regex_whitespace_with_closing_curly_brace)) {
 				parser.allow_whitespace();
 			} else {
 				parser.require_whitespace();
@@ -350,7 +352,7 @@ export default function mustache(parser: Parser) {
 		let identifiers;
 
 		// Implies {@debug} which indicates "debug all"
-		if (parser.read(/\s*}/)) {
+		if (parser.read(regex_whitespace_with_closing_curly_brace)) {
 			identifiers = [];
 		} else {
 			const expression = read_expression(parser);
diff --git a/src/compiler/parse/state/tag.ts b/src/compiler/parse/state/tag.ts
index efce375b7e..9d1bf5e5c2 100644
--- a/src/compiler/parse/state/tag.ts
+++ b/src/compiler/parse/state/tag.ts
@@ -53,13 +53,17 @@ function parent_is_head(stack) {
 	return false;
 }
 
+const regex_closing_textarea_tag = /^<\/textarea(\s[^>]*)?>/i;
+const regex_closing_comment = /-->/;
+const regex_capital_letter = /[A-Z]/;
+
 export default function tag(parser: Parser) {
 	const start = parser.index++;
 
 	let parent = parser.current();
 
 	if (parser.eat('!--')) {
-		const data = parser.read_until(/-->/);
+		const data = parser.read_until(regex_closing_comment);
 		parser.eat('-->', true, parser_errors.unclosed_comment);
 
 		parser.current().children.push({
@@ -104,7 +108,7 @@ export default function tag(parser: Parser) {
 
 	const type = meta_tags.has(name)
 		? meta_tags.get(name)
-		: (/[A-Z]/.test(name[0]) || name === 'svelte:self' || name === 'svelte:component') ? 'InlineComponent'
+		: (regex_capital_letter.test(name[0]) || name === 'svelte:self' || name === 'svelte:component') ? 'InlineComponent'
 			: name === 'svelte:fragment' ? 'SlotTemplate'
 				: name === 'title' && parent_is_head(parser.stack) ? 'Title'
 					: name === 'slot' && !parser.customElement ? 'Slot' : 'Element';
@@ -218,10 +222,10 @@ export default function tag(parser: Parser) {
 		// special case
 		element.children = read_sequence(
 			parser,
-			() =>
-				/^<\/textarea(\s[^>]*)?>/i.test(parser.template.slice(parser.index))
+			() => regex_closing_textarea_tag.test(parser.template.slice(parser.index)),
+			'inside <textarea>'
 		);
-		parser.read(/^<\/textarea(\s[^>]*)?>/i);
+		parser.read(regex_closing_textarea_tag);
 		element.end = parser.index;
 	} else if (name === 'script' || name === 'style') {
 		// special case
@@ -236,6 +240,8 @@ export default function tag(parser: Parser) {
 	}
 }
 
+const regex_whitespace_or_slash_or_closing_tag = /(\s|\/|>)/;
+
 function read_tag_name(parser: Parser) {
 	const start = parser.index;
 
@@ -265,7 +271,7 @@ function read_tag_name(parser: Parser) {
 
 	if (parser.read(SLOT)) return 'svelte:fragment';
 
-	const name = parser.read_until(/(\s|\/|>)/);
+	const name = parser.read_until(regex_whitespace_or_slash_or_closing_tag);
 
 	if (meta_tags.has(name)) return name;
 
@@ -285,6 +291,10 @@ function read_tag_name(parser: Parser) {
 	return name;
 }
 
+// eslint-disable-next-line no-useless-escape
+const regex_token_ending_character = /[\s=\/>"']/;
+const regex_quote_characters = /["']/;
+
 function read_attribute(parser: Parser, unique_names: Set<string>) {
 	const start = parser.index;
 
@@ -343,8 +353,7 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 		}
 	}
 
-	// eslint-disable-next-line no-useless-escape
-	const name = parser.read_until(/[\s=\/>"']/);
+	const name = parser.read_until(regex_token_ending_character);
 	if (!name) return null;
 
 	let end = parser.index;
@@ -359,7 +368,7 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 		parser.allow_whitespace();
 		value = read_attribute_value(parser);
 		end = parser.index;
-	} else if (parser.match_regex(/["']/)) {
+	} else if (parser.match_regex(regex_quote_characters)) {
 		parser.error(parser_errors.unexpected_token('='), parser.index);
 	}
 
@@ -386,6 +395,7 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 				end,
 				type,
 				name: directive_name,
+				modifiers,
 				value
 			};
 		}
@@ -473,7 +483,7 @@ function read_attribute_value(parser: Parser) {
 
 	let value;
 	try {
-		value = read_sequence(parser, () => !!parser.match_regex(regex));
+		value = read_sequence(parser, () => !!parser.match_regex(regex), 'in attribute value');
 	} catch (error) {
 		if (error.code === 'parse-error') {
 			// if the attribute value didn't close + self-closing tag
@@ -495,7 +505,7 @@ function read_attribute_value(parser: Parser) {
 	return value;
 }
 
-function read_sequence(parser: Parser, done: () => boolean): TemplateNode[] {
+function read_sequence(parser: Parser, done: () => boolean, location: string): TemplateNode[] {
 	let current_chunk: Text = {
 		start: parser.index,
 		end: null,
@@ -521,6 +531,18 @@ function read_sequence(parser: Parser, done: () => boolean): TemplateNode[] {
 			flush(parser.index);
 			return chunks;
 		} else if (parser.eat('{')) {
+			if (parser.match('#')) {
+				const index = parser.index - 1;
+				parser.eat('#');
+				const name = parser.read_until(/[^a-z]/);
+				parser.error(parser_errors.invalid_logic_block_placement(location, name), index);
+			} else if (parser.match('@')) {
+				const index = parser.index - 1;
+				parser.eat('@');
+				const name = parser.read_until(/[^a-z]/);
+				parser.error(parser_errors.invalid_tag_placement(location, name), index);
+			}
+
 			flush(parser.index - 1);
 
 			parser.allow_whitespace();
diff --git a/src/compiler/preprocess/index.ts b/src/compiler/preprocess/index.ts
index ab2ede29e0..45885afa96 100644
--- a/src/compiler/preprocess/index.ts
+++ b/src/compiler/preprocess/index.ts
@@ -4,6 +4,7 @@ import { MappedCode, SourceLocation, parse_attached_sourcemap, sourcemap_add_off
 import { decode_map } from './decode_sourcemap';
 import { replace_in_code, slice_source } from './replace_in_code';
 import { MarkupPreprocessor, Source, Preprocessor, PreprocessorGroup, Processed } from './types';
+import { regex_whitespaces } from '../utils/patterns';
 
 export * from './types';
 
@@ -13,8 +14,10 @@ interface SourceUpdate {
 	dependencies?: string[];
 }
 
+const regex_filepath_separator = /[/\\]/;
+
 function get_file_basename(filename: string) {
-	return filename.split(/[/\\]/).pop();
+	return filename.split(regex_filepath_separator).pop();
 }
 
 /**
@@ -120,20 +123,26 @@ function processed_tag_to_code(
 	return tag_open_code.concat(content_code).concat(tag_close_code);
 }
 
+const regex_quoted_value = /^['"](.*)['"]$/;
+
 function parse_tag_attributes(str: string) {
 	// note: won't work with attribute values containing spaces.
 	return str
-		.split(/\s+/)
+		.split(regex_whitespaces)
 		.filter(Boolean)
 		.reduce((attrs, attr) => {
 			const i = attr.indexOf('=');
 			const [key, value] = i > 0 ? [attr.slice(0, i), attr.slice(i + 1)] : [attr];
-			const [, unquoted] = (value && value.match(/^['"](.*)['"]$/)) || [];
+			const [, unquoted] = (value && value.match(regex_quoted_value)) || [];
 
 			return { ...attrs, [key]: unquoted ?? value ?? true };
 		}, {});
 }
 
+
+const regex_style_tags = /<!--[^]*?-->|<style(\s[^]*?)?(?:>([^]*?)<\/style>|\/>)/gi;
+const regex_script_tags = /<!--[^]*?-->|<script(\s[^]*?)?(?:>([^]*?)<\/script>|\/>)/gi;
+
 /**
  * Calculate the updates required to process all instances of the specified tag.
  */
@@ -143,10 +152,7 @@ async function process_tag(
 	source: Source
 ): Promise<SourceUpdate> {
 	const { filename, source: markup } = source;
-	const tag_regex =
-		tag_name === 'style'
-			? /<!--[^]*?-->|<style(\s[^]*?)?(?:>([^]*?)<\/style>|\/>)/gi
-			: /<!--[^]*?-->|<script(\s[^]*?)?(?:>([^]*?)<\/script>|\/>)/gi;
+	const tag_regex = tag_name === 'style' ? regex_style_tags : regex_script_tags;
 
 	const dependencies: string[] = [];
 
@@ -190,7 +196,7 @@ async function process_markup(process: MarkupPreprocessor, source: Source) {
 			string: processed.code,
 			map: processed.map
 				? // TODO: can we use decode_sourcemap?
-				  typeof processed.map === 'string'
+				typeof processed.map === 'string'
 					? JSON.parse(processed.map)
 					: processed.map
 				: undefined,
diff --git a/src/compiler/utils/extract_svelte_ignore.ts b/src/compiler/utils/extract_svelte_ignore.ts
index 306ba872d6..30be2893a4 100644
--- a/src/compiler/utils/extract_svelte_ignore.ts
+++ b/src/compiler/utils/extract_svelte_ignore.ts
@@ -1,11 +1,12 @@
 import { TemplateNode } from '../interfaces';
 import { flatten } from './flatten';
+import { regex_whitespace } from './patterns';
 
-const pattern = /^\s*svelte-ignore\s+([\s\S]+)\s*$/m;
+const regex_svelte_ignore = /^\s*svelte-ignore\s+([\s\S]+)\s*$/m;
 
 export function extract_svelte_ignore(text: string): string[] {
-	const match = pattern.exec(text);
-	return match ? match[1].split(/[^\S]/).map(x => x.trim()).filter(Boolean) : [];
+	const match = regex_svelte_ignore.exec(text);
+	return match ? match[1].split(regex_whitespace).map(x => x.trim()).filter(Boolean) : [];
 }
 
 export function extract_svelte_ignore_from_comments<Node extends { leadingComments?: Array<{value: string}> }>(node: Node): string[] {
diff --git a/src/compiler/utils/get_code_frame.ts b/src/compiler/utils/get_code_frame.ts
index 1097f5b3d2..14ca44badb 100644
--- a/src/compiler/utils/get_code_frame.ts
+++ b/src/compiler/utils/get_code_frame.ts
@@ -1,5 +1,7 @@
+const regex_tabs = /^\t+/;
+
 function tabs_to_spaces(str: string) {
-	return str.replace(/^\t+/, match => match.split('\t').join('  '));
+	return str.replace(regex_tabs, match => match.split('\t').join('  '));
 }
 
 export default function get_code_frame(
diff --git a/src/compiler/utils/mapped_code.ts b/src/compiler/utils/mapped_code.ts
index 04fa05be9a..bf7b016fc5 100644
--- a/src/compiler/utils/mapped_code.ts
+++ b/src/compiler/utils/mapped_code.ts
@@ -61,6 +61,8 @@ function merge_tables<T>(this_table: T[], other_table: T[]): [T[], number[], boo
 	return [new_table, idx_map, val_changed, idx_changed];
 }
 
+const regex_line_token = /([^\d\w\s]|\s+)/g;
+
 export class MappedCode {
 	string: string;
 	map: DecodedSourceMap;
@@ -195,7 +197,7 @@ export class MappedCode {
 		const line_list = source.split('\n');
 		for (let line = 0; line < line_list.length; line++) {
 			map.mappings.push([]);
-			const token_list = line_list[line].split(/([^\d\w\s]|\s+)/g);
+			const token_list = line_list[line].split(regex_line_token);
 			for (let token = 0, column = 0; token < token_list.length; token++) {
 				if (token_list[token] == '') continue;
 				map.mappings[line].push([column, 0, offset.line + line, column]);
@@ -245,7 +247,7 @@ export function combine_sourcemaps(
 	if (!map.file) delete map.file; // skip optional field `file`
 
 	// When source maps are combined and the leading map is empty, sources is not set.
-	// Add the filename to the empty array in this case. 
+	// Add the filename to the empty array in this case.
 	// Further improvements to remapping may help address this as well https://github.com/ampproject/remapping/issues/116
 	if (!map.sources.length) map.sources = [filename];
 
@@ -289,6 +291,8 @@ export function apply_preprocessor_sourcemap(filename: string, svelte_map: Sourc
 	return result_map as SourceMap;
 }
 
+const regex_data_uri = /data:(?:application|text)\/json;(?:charset[:=]\S+?;)?base64,(\S*)/;
+
 // parse attached sourcemap in processed.code
 export function parse_attached_sourcemap(processed: Processed, tag_name: 'script' | 'style'): void {
 	const r_in = '[#@]\\s*sourceMappingURL\\s*=\\s*(\\S*)';
@@ -302,7 +306,7 @@ export function parse_attached_sourcemap(processed: Processed, tag_name: 'script
 	}
 	processed.code = processed.code.replace(regex, (_, match1, match2) => {
 		const map_url = (tag_name == 'script') ? (match1 || match2) : match1;
-		const map_data = (map_url.match(/data:(?:application|text)\/json;(?:charset[:=]\S+?;)?base64,(\S*)/) || [])[1];
+		const map_data = (map_url.match(regex_data_uri) || [])[1];
 		if (map_data) {
 			// sourceMappingURL is data URL
 			if (processed.map) {
diff --git a/src/compiler/utils/names.ts b/src/compiler/utils/names.ts
index 9d5b78fceb..303c6297b0 100644
--- a/src/compiler/utils/names.ts
+++ b/src/compiler/utils/names.ts
@@ -1,5 +1,6 @@
 import { isIdentifierStart, isIdentifierChar } from 'acorn';
 import full_char_code_at from './full_char_code_at';
+import { regex_starts_with_underscore, regex_ends_with_underscore } from './patterns';
 
 export const reserved = new Set([
 	'arguments',
@@ -65,10 +66,13 @@ export function is_valid(str: string): boolean {
 	return true;
 }
 
+const regex_non_standard_characters = /[^a-zA-Z0-9_]+/g;
+const regex_starts_with_number = /^[0-9]/;
+
 export function sanitize(name: string) {
 	return name
-		.replace(/[^a-zA-Z0-9_]+/g, '_')
-		.replace(/^_/, '')
-		.replace(/_$/, '')
-		.replace(/^[0-9]/, '_$&');
+		.replace(regex_non_standard_characters, '_')
+		.replace(regex_starts_with_underscore, '')
+		.replace(regex_ends_with_underscore, '')
+		.replace(regex_starts_with_number, '_$&');
 }
diff --git a/src/compiler/utils/patterns.ts b/src/compiler/utils/patterns.ts
index 071abd791f..9429d47227 100644
--- a/src/compiler/utils/patterns.ts
+++ b/src/compiler/utils/patterns.ts
@@ -1,6 +1,24 @@
-export const whitespace = /[ \t\r\n]/;
-export const start_whitespace = /^[ \t\r\n]*/;
-export const end_whitespace = /[ \t\r\n]*$/;
-export const start_newline = /^\r?\n/;
+export const regex_whitespace = /\s/;
+export const regex_whitespaces = /\s+/;
+export const regex_starts_with_whitespace = /^\s/;
+export const regex_starts_with_whitespaces = /^[ \t\r\n]*/;
+export const regex_ends_with_whitespace = /\s$/;
+export const regex_ends_with_whitespaces = /[ \t\r\n]*$/;
+export const regex_only_whitespaces = /^\s+$/;
 
-export const dimensions = /^(?:offset|client)(?:Width|Height)$/;
+export const regex_whitespace_characters = /\s/g;
+export const regex_non_whitespace_character = /\S/;
+
+export const regex_starts_with_newline = /^\r?\n/;
+export const regex_not_newline_characters = /[^\n]/g;
+
+export const regex_double_quotes = /"/g;
+
+export const regex_backslashes = /\\/g;
+
+export const regex_starts_with_underscore = /^_/;
+export const regex_ends_with_underscore = /_$/;
+
+export const regex_invalid_variable_identifier_characters = /[^a-zA-Z0-9_$]/g;
+
+export const regex_dimensions = /^(?:offset|client)(?:Width|Height)$/;
diff --git a/src/compiler/utils/trim.ts b/src/compiler/utils/trim.ts
index 05af79cc90..919a423d7f 100644
--- a/src/compiler/utils/trim.ts
+++ b/src/compiler/utils/trim.ts
@@ -1,9 +1,9 @@
-import { start_whitespace, end_whitespace } from './patterns';
+import { regex_starts_with_whitespaces, regex_ends_with_whitespaces } from './patterns';
 
 export function trim_start(str: string) {
-	return str.replace(start_whitespace, '');
+	return str.replace(regex_starts_with_whitespaces, '');
 }
 
 export function trim_end(str: string) {
-	return str.replace(end_whitespace, '');
+	return str.replace(regex_ends_with_whitespaces, '');
 }
diff --git a/src/runtime/internal/lifecycle.ts b/src/runtime/internal/lifecycle.ts
index fbbeca9a67..e75bbdc501 100644
--- a/src/runtime/internal/lifecycle.ts
+++ b/src/runtime/internal/lifecycle.ts
@@ -11,18 +11,47 @@ export function get_current_component() {
 	return current_component;
 }
 
+/**
+ * Schedules a callback to run immediately before the component is updated after any state change.
+ * 
+ * The first time the callback runs will be before the initial `onMount`
+ * 
+ * https://svelte.dev/docs#run-time-svelte-beforeupdate
+ */
 export function beforeUpdate(fn: () => any) {
 	get_current_component().$$.before_update.push(fn);
 }
 
+/**
+ * The `onMount` function schedules a callback to run as soon as the component has been mounted to the DOM. 
+ * It must be called during the component's initialisation (but doesn't need to live *inside* the component; 
+ * it can be called from an external module).
+ * 
+ * `onMount` does not run inside a [server-side component](/docs#run-time-server-side-component-api).
+ * 
+ * https://svelte.dev/docs#run-time-svelte-onmount
+ */
 export function onMount(fn: () => any) {
 	get_current_component().$$.on_mount.push(fn);
 }
 
+/**
+ * Schedules a callback to run immediately after the component has been updated.
+ * 
+ * The first time the callback runs will be after the initial `onMount` 
+ */
 export function afterUpdate(fn: () => any) {
 	get_current_component().$$.after_update.push(fn);
 }
 
+/** 
+ * Schedules a callback to run immediately before the component is unmounted.
+ * 
+ * Out of `onMount`, `beforeUpdate`, `afterUpdate` and `onDestroy`, this is the 
+ * only one that runs inside a server-side component.
+ * 
+ * https://svelte.dev/docs#run-time-svelte-ondestroy
+ */
 export function onDestroy(fn: () => any) {
 	get_current_component().$$.on_destroy.push(fn);
 }
@@ -31,6 +60,18 @@ export interface DispatchOptions {
 	cancelable?: boolean;
 }
 
+/**
+ * Creates an event dispatcher that can be used to dispatch [component events](/docs#template-syntax-component-directives-on-eventname). 
+ * Event dispatchers are functions that can take two arguments: `name` and `detail`.
+ * 
+ * Component events created with `createEventDispatcher` create a 
+ * [CustomEvent](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent). 
+ * These events do not [bubble](https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Building_blocks/Events#Event_bubbling_and_capture).
+ * The `detail` argument corresponds to the [CustomEvent.detail](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/detail) 
+ * property and can contain any type of data. 
+ * 
+ * https://svelte.dev/docs#run-time-svelte-createeventdispatcher
+ */
 export function createEventDispatcher<EventMap extends {} = any>(): <
 	EventKey extends Extract<keyof EventMap, string>
 >(
@@ -57,19 +98,47 @@ export function createEventDispatcher<EventMap extends {} = any>(): <
 	};
 }
 
+/**
+ * Associates an arbitrary `context` object with the current component and the specified `key` 
+ * and returns that object. The context is then available to children of the component 
+ * (including slotted content) with `getContext`.
+ * 
+ * Like lifecycle functions, this must be called during component initialisation. 
+ * 
+ * https://svelte.dev/docs#run-time-svelte-setcontext
+ */
 export function setContext<T>(key, context: T): T {
 	get_current_component().$$.context.set(key, context);
 	return context;
 }
 
+/**
+ * Retrieves the context that belongs to the closest parent component with the specified `key`. 
+ * Must be called during component initialisation. 
+ * 
+ * https://svelte.dev/docs#run-time-svelte-getcontext
+ */
 export function getContext<T>(key): T {
 	return get_current_component().$$.context.get(key);
 }
 
+/**
+ * Retrieves the whole context map that belongs to the closest parent component. 
+ * Must be called during component initialisation. Useful, for example, if you 
+ * programmatically create a component and want to pass the existing context to it.
+ * 
+ * https://svelte.dev/docs#run-time-svelte-getallcontexts
+ */
 export function getAllContexts<T extends Map<any, any> = Map<any, any>>(): T {
 	return get_current_component().$$.context;
 }
 
+/**
+ * Checks whether a given `key` has been set in the context of a parent component. 
+ * Must be called during component initialisation. 
+ * 
+ * https://svelte.dev/docs#run-time-svelte-hascontext
+ */
 export function hasContext(key): boolean {
 	return get_current_component().$$.context.has(key);	
 }
diff --git a/test/js/samples/unchanged-expression/expected.js b/test/js/samples/unchanged-expression/expected.js
index 48ae8131ff..8ede703cec 100644
--- a/test/js/samples/unchanged-expression/expected.js
+++ b/test/js/samples/unchanged-expression/expected.js
@@ -73,7 +73,7 @@ let world1 = 'world';
 let world2 = 'world';
 
 function instance($$self, $$props, $$invalidate) {
-	const world3 = 'world';
+	let world3 = 'world';
 
 	function foo() {
 		$$invalidate(0, world3 = 'svelte');
diff --git a/test/js/samples/unchanged-expression/input.svelte b/test/js/samples/unchanged-expression/input.svelte
index 057201358c..35fa8b65d3 100644
--- a/test/js/samples/unchanged-expression/input.svelte
+++ b/test/js/samples/unchanged-expression/input.svelte
@@ -1,7 +1,7 @@
 <script>
   let world1 = 'world';
   let world2 = 'world';
-  const world3 = 'world';
+  let world3 = 'world';
   function foo() {
     world3 = 'svelte';
   }
diff --git a/test/parser/samples/attribute-style-directive-modifiers/input.svelte b/test/parser/samples/attribute-style-directive-modifiers/input.svelte
new file mode 100644
index 0000000000..1ec740107d
--- /dev/null
+++ b/test/parser/samples/attribute-style-directive-modifiers/input.svelte
@@ -0,0 +1 @@
+<div style:color|important={myColor}></div>
\ No newline at end of file
diff --git a/test/parser/samples/attribute-style-directive-modifiers/output.json b/test/parser/samples/attribute-style-directive-modifiers/output.json
new file mode 100644
index 0000000000..3c607fb5ea
--- /dev/null
+++ b/test/parser/samples/attribute-style-directive-modifiers/output.json
@@ -0,0 +1,50 @@
+{
+	"html": {
+		"start": 0,
+		"end": 43,
+		"type": "Fragment",
+		"children": [
+			{
+				"start": 0,
+				"end": 43,
+				"type": "Element",
+				"name": "div",
+				"attributes": [
+					{
+						"start": 5,
+						"end": 36,
+						"type": "StyleDirective",
+						"name": "color",
+						"modifiers": [
+							"important"
+						],
+						"value": [
+							{
+								"start": 27,
+								"end": 36,
+								"type": "MustacheTag",
+								"expression": {
+									"type": "Identifier",
+									"start": 28,
+									"end": 35,
+									"loc": {
+										"start": {
+											"line": 1,
+											"column": 28
+										},
+										"end": {
+											"line": 1,
+											"column": 35
+										}
+									},
+									"name": "myColor"
+								}
+							}
+						]
+					}
+				],
+				"children": []
+			}
+		]
+	}
+}
\ No newline at end of file
diff --git a/test/parser/samples/attribute-style-directive-shorthand/output.json b/test/parser/samples/attribute-style-directive-shorthand/output.json
index ac658408e6..80fb4f741f 100644
--- a/test/parser/samples/attribute-style-directive-shorthand/output.json
+++ b/test/parser/samples/attribute-style-directive-shorthand/output.json
@@ -15,6 +15,7 @@
 						"end": 16,
 						"type": "StyleDirective",
 						"name": "color",
+						"modifiers": [],
 						"value": true
 					}
 				],
@@ -22,4 +23,4 @@
 			}
 		]
 	}
-}
\ No newline at end of file
+}
diff --git a/test/parser/samples/attribute-style-directive-string/output.json b/test/parser/samples/attribute-style-directive-string/output.json
index e81e7be3c9..505e9333e1 100644
--- a/test/parser/samples/attribute-style-directive-string/output.json
+++ b/test/parser/samples/attribute-style-directive-string/output.json
@@ -15,6 +15,7 @@
 						"end": 22,
 						"type": "StyleDirective",
 						"name": "color",
+						"modifiers": [],
 						"value": [
 							{
 								"start": 18,
@@ -45,6 +46,7 @@
 						"start": 35,
 						"end": 52,
 						"type": "StyleDirective",
+						"modifiers": [],
 						"name": "color",
 						"value": [
 							{
@@ -77,6 +79,7 @@
 						"end": 80,
 						"type": "StyleDirective",
 						"name": "color",
+						"modifiers": [],
 						"value": [
 							{
 								"start": 77,
@@ -108,6 +111,7 @@
 						"end": 120,
 						"type": "StyleDirective",
 						"name": "color",
+						"modifiers": [],
 						"value": [
 							{
 								"start": 106,
@@ -160,6 +164,7 @@
 						"end": 160,
 						"type": "StyleDirective",
 						"name": "color",
+						"modifiers": [],
 						"value": [
 							{
 								"start": 146,
@@ -212,6 +217,7 @@
 						"end": 198,
 						"type": "StyleDirective",
 						"name": "color",
+						"modifiers": [],
 						"value": [
 							{
 								"start": 185,
@@ -264,6 +270,7 @@
 						"end": 245,
 						"type": "StyleDirective",
 						"name": "color",
+						"modifiers": [],
 						"value": [
 							{
 								"start": 223,
@@ -352,4 +359,4 @@
 			}
 		]
 	}
-}
\ No newline at end of file
+}
diff --git a/test/parser/samples/attribute-style-directive/output.json b/test/parser/samples/attribute-style-directive/output.json
index f36ce6b01e..d80d61bddb 100644
--- a/test/parser/samples/attribute-style-directive/output.json
+++ b/test/parser/samples/attribute-style-directive/output.json
@@ -15,6 +15,7 @@
 						"end": 26,
 						"type": "StyleDirective",
 						"name": "color",
+						"modifiers": [],
 						"value": [
 							{
 								"start": 17,
diff --git a/test/parser/samples/error-css/error.json b/test/parser/samples/error-css/error.json
index 90f7a091d2..78bea3030c 100644
--- a/test/parser/samples/error-css/error.json
+++ b/test/parser/samples/error-css/error.json
@@ -1,6 +1,6 @@
 {
 	"code": "css-syntax-error",
-	"message": "LeftCurlyBracket is expected",
+	"message": "\"{\" is expected",
 	"start": {
 		"line": 2,
 		"column": 16,
diff --git a/test/runtime-puppeteer/samples/inline-style-directive-important/_config.js b/test/runtime-puppeteer/samples/inline-style-directive-important/_config.js
new file mode 100644
index 0000000000..d6323b82e3
--- /dev/null
+++ b/test/runtime-puppeteer/samples/inline-style-directive-important/_config.js
@@ -0,0 +1,22 @@
+export default {
+	html: `
+		<h1 class="svelte-szzkfu" style="background-color: red;">hello</h1>
+		<h1 class="svelte-szzkfu" style="background-color: red !important;">hello</h1>
+	`,
+
+	ssrHtml: `
+		<h1 class="svelte-szzkfu" style="background-color: red;">hello</h1>
+		<h1 class="svelte-szzkfu" style="background-color: red !important;">hello</h1>
+	`,
+	
+	test({ assert, target, window, component }) {
+		const h1s = target.querySelectorAll('h1');
+
+		assert.equal(window.getComputedStyle(h1s[0])['backgroundColor'], 'rgb(0, 0, 255)');
+		assert.equal(window.getComputedStyle(h1s[1])['backgroundColor'], 'rgb(255, 0, 0)');
+
+		component.color = 'yellow';
+		assert.equal(window.getComputedStyle(h1s[0])['backgroundColor'], 'rgb(0, 0, 255)');
+		assert.equal(window.getComputedStyle(h1s[1])['backgroundColor'], 'rgb(255, 255, 0)');
+	}
+};
diff --git a/test/runtime-puppeteer/samples/inline-style-directive-important/main.svelte b/test/runtime-puppeteer/samples/inline-style-directive-important/main.svelte
new file mode 100644
index 0000000000..e869a9a473
--- /dev/null
+++ b/test/runtime-puppeteer/samples/inline-style-directive-important/main.svelte
@@ -0,0 +1,12 @@
+<script>
+	export let color = 'red'
+</script>
+
+<h1 style:background-color={color} >hello</h1>
+<h1 style:background-color|important="{color}">hello</h1>
+
+<style>
+	h1 {
+		background-color: blue !important;
+	}
+</style> 
\ No newline at end of file
diff --git a/test/server-side-rendering/index.ts b/test/server-side-rendering/index.ts
index 2a4e0596e7..a5458be109 100644
--- a/test/server-side-rendering/index.ts
+++ b/test/server-side-rendering/index.ts
@@ -117,7 +117,9 @@ describe('ssr', () => {
 					fs.writeFileSync(`${dir}/_actual-head.html`, head);
 
 					try {
-						assert.htmlEqual(
+						(compileOptions.hydratable
+							? assert.htmlEqualWithComments
+							: assert.htmlEqual)(
 							head,
 							fs.readFileSync(`${dir}/_expected-head.html`, 'utf-8')
 						);
diff --git a/test/server-side-rendering/samples/head-meta-hydrate-duplicate/_config.js b/test/server-side-rendering/samples/head-meta-hydrate-duplicate/_config.js
index ae9b250f86..f1f4fff921 100644
--- a/test/server-side-rendering/samples/head-meta-hydrate-duplicate/_config.js
+++ b/test/server-side-rendering/samples/head-meta-hydrate-duplicate/_config.js
@@ -1,5 +1,6 @@
 export default {
 	compileOptions: {
 		hydratable: true
-	}
+	},
+	withoutNormalizeHtml: true
 };
diff --git a/test/validator/samples/a11y-no-nointeractive-tabindex/warnings.json b/test/validator/samples/a11y-no-nointeractive-tabindex/warnings.json
index 97b8ccd9b3..740d9b346c 100644
--- a/test/validator/samples/a11y-no-nointeractive-tabindex/warnings.json
+++ b/test/validator/samples/a11y-no-nointeractive-tabindex/warnings.json
@@ -6,7 +6,7 @@
 			"column": 20,
 			"line": 11
 		},
-		"message": "A11y: not interactive element cannot have positive tabIndex value",
+		"message": "A11y: noninteractive element cannot have positive tabIndex value",
 		"pos": 221,
 		"start": {
 			"character": 221,
@@ -21,7 +21,7 @@
 			"column": 35,
 			"line": 12
 		},
-		"message": "A11y: not interactive element cannot have positive tabIndex value",
+		"message": "A11y: noninteractive element cannot have positive tabIndex value",
 		"pos": 242,
 		"start": {
 			"character": 242,
@@ -36,7 +36,7 @@
 			"column": 24,
 			"line": 13
 		},
-		"message": "A11y: not interactive element cannot have positive tabIndex value",
+		"message": "A11y: noninteractive element cannot have positive tabIndex value",
 		"pos": 278,
 		"start": {
 			"character": 278,
@@ -51,7 +51,7 @@
 			"column": 26,
 			"line": 14
 		},
-		"message": "A11y: not interactive element cannot have positive tabIndex value",
+		"message": "A11y: noninteractive element cannot have positive tabIndex value",
 		"pos": 303,
 		"start": {
 			"character": 303,
diff --git a/test/validator/samples/assignment-to-const-2/errors.json b/test/validator/samples/assignment-to-const-2/errors.json
new file mode 100644
index 0000000000..b8da2a3d8e
--- /dev/null
+++ b/test/validator/samples/assignment-to-const-2/errors.json
@@ -0,0 +1,17 @@
+[
+	{
+		"code": "assignment-to-const",
+		"message": "You are assigning to a const",
+		"start": {
+			"line": 13,
+			"column": 24,
+			"character": 282
+		},
+		"end": {
+			"line": 13,
+			"column": 35,
+			"character": 293
+		},
+		"pos": 282
+	}
+]
\ No newline at end of file
diff --git a/test/validator/samples/assignment-to-const-2/input.svelte b/test/validator/samples/assignment-to-const-2/input.svelte
new file mode 100644
index 0000000000..433c6d0076
--- /dev/null
+++ b/test/validator/samples/assignment-to-const-2/input.svelte
@@ -0,0 +1,15 @@
+<script>
+	const immutable = 0;
+
+	const obj1 = { prop: true };
+	const obj2 = { prop: 0 }
+</script>
+
+<!-- should not error -->
+<button on:click={() => obj1.prop = false}>click</button>
+<button on:click={() => obj2.prop++}>click</button>
+
+<!-- should error -->
+<button on:click={() => immutable++}>click</button>
+
+
diff --git a/test/validator/samples/assignment-to-const-3/errors.json b/test/validator/samples/assignment-to-const-3/errors.json
new file mode 100644
index 0000000000..4842d55dc3
--- /dev/null
+++ b/test/validator/samples/assignment-to-const-3/errors.json
@@ -0,0 +1,17 @@
+[
+	{
+		"code": "assignment-to-const",
+		"message": "You are assigning to a const",
+		"start": {
+			"line": 14,
+			"column": 3,
+			"character": 172
+		},
+		"end": {
+			"line": 14,
+			"column": 10,
+			"character": 179
+		},
+		"pos": 172
+	}
+]
\ No newline at end of file
diff --git a/test/validator/samples/assignment-to-const-3/input.svelte b/test/validator/samples/assignment-to-const-3/input.svelte
new file mode 100644
index 0000000000..faaf448823
--- /dev/null
+++ b/test/validator/samples/assignment-to-const-3/input.svelte
@@ -0,0 +1,20 @@
+<script>
+	const foo = 'hello';
+	
+	function shouldNotError() {
+		let foo = 0;
+		
+		function inner() {
+			foo = 1;
+		}
+	}
+	
+	function shouldError() {
+		function inner() {
+			foo = 1;
+		}
+	}
+</script>
+
+<button on:click={shouldNotError}>click</button>
+<button on:click={shouldError}>click</button>
\ No newline at end of file
diff --git a/test/validator/samples/assignment-to-const-4/errors.json b/test/validator/samples/assignment-to-const-4/errors.json
new file mode 100644
index 0000000000..aa97538a60
--- /dev/null
+++ b/test/validator/samples/assignment-to-const-4/errors.json
@@ -0,0 +1,17 @@
+[
+	{
+		"code": "assignment-to-const",
+		"message": "You are assigning to a const",
+		"start": {
+			"line": 17,
+			"column": 2,
+			"character": 189
+		},
+		"end": {
+			"line": 17,
+			"column": 9,
+			"character": 196
+		},
+		"pos": 189
+	}
+]
\ No newline at end of file
diff --git a/test/validator/samples/assignment-to-const-4/input.svelte b/test/validator/samples/assignment-to-const-4/input.svelte
new file mode 100644
index 0000000000..12229132bf
--- /dev/null
+++ b/test/validator/samples/assignment-to-const-4/input.svelte
@@ -0,0 +1,21 @@
+<script>
+	const foo = 'hello';
+</script>
+
+<button on:click={() => {
+	let foo = 0;
+		
+	function inner() {
+		foo = 1;
+	}
+}}>
+	click
+</button>
+
+<button on:click={() => {
+	function inner() {
+		foo = 1;
+	}
+}}>
+	click
+</button>
\ No newline at end of file
diff --git a/test/validator/samples/assignment-to-const/errors.json b/test/validator/samples/assignment-to-const/errors.json
new file mode 100644
index 0000000000..7f4f264f1d
--- /dev/null
+++ b/test/validator/samples/assignment-to-const/errors.json
@@ -0,0 +1,17 @@
+[
+	{
+		"code": "assignment-to-const",
+		"message": "You are assigning to a const",
+		"start": {
+			"line": 16,
+			"column": 2,
+			"character": 225
+		},
+		"end": {
+			"line": 16,
+			"column": 18,
+			"character": 241
+		},
+		"pos": 225
+	}
+]
\ No newline at end of file
diff --git a/test/validator/samples/assignment-to-const/input.svelte b/test/validator/samples/assignment-to-const/input.svelte
new file mode 100644
index 0000000000..d570e7c86b
--- /dev/null
+++ b/test/validator/samples/assignment-to-const/input.svelte
@@ -0,0 +1,24 @@
+<script>
+	const immutable = false;
+
+	const obj1 = { prop: true };
+	const obj2 = { prop: 0 };
+
+	function shouldNotError() {
+		obj1.prop = false;
+	}
+
+	function shouldNotError2() {
+		obj2.prop++;
+	}
+
+	function shouldError() {
+		immutable = true
+	}
+
+	
+</script>
+
+<button on:click={shouldNotError}>click</button>
+<button on:click={shouldNotError2}>click</button>
+<button on:click={shouldError}>click</button>
diff --git a/test/validator/samples/html-block-in-attribute/errors.json b/test/validator/samples/html-block-in-attribute/errors.json
new file mode 100644
index 0000000000..7cfe43dc0b
--- /dev/null
+++ b/test/validator/samples/html-block-in-attribute/errors.json
@@ -0,0 +1,9 @@
+[
+	{
+		"code": "invalid-tag-placement",
+		"message": "{@html} tag cannot be in attribute value",
+		"start": { "line": 1, "column": 12, "character": 12 },
+		"end": { "line": 1, "column": 12, "character": 12 },
+		"pos": 12
+	}
+]
diff --git a/test/validator/samples/html-block-in-attribute/input.svelte b/test/validator/samples/html-block-in-attribute/input.svelte
new file mode 100644
index 0000000000..46b8ca5b7e
--- /dev/null
+++ b/test/validator/samples/html-block-in-attribute/input.svelte
@@ -0,0 +1 @@
+<div style="{@html text}" />
\ No newline at end of file
diff --git a/test/validator/samples/html-block-in-textarea/errors.json b/test/validator/samples/html-block-in-textarea/errors.json
new file mode 100644
index 0000000000..756fa5ad3e
--- /dev/null
+++ b/test/validator/samples/html-block-in-textarea/errors.json
@@ -0,0 +1,9 @@
+[
+	{
+		"code": "invalid-tag-placement",
+		"message": "{@html} tag cannot be inside <textarea>",
+		"start": { "line": 2, "column": 1, "character": 12 },
+		"end": { "line": 2, "column": 1, "character": 12 },
+		"pos": 12
+	}
+]
diff --git a/test/validator/samples/html-block-in-textarea/input.svelte b/test/validator/samples/html-block-in-textarea/input.svelte
new file mode 100644
index 0000000000..5da8dbf75a
--- /dev/null
+++ b/test/validator/samples/html-block-in-textarea/input.svelte
@@ -0,0 +1,3 @@
+<textarea>
+	{@html fruit}
+</textarea>
\ No newline at end of file
diff --git a/test/validator/samples/logic-block-in-attribute/errors.json b/test/validator/samples/logic-block-in-attribute/errors.json
new file mode 100644
index 0000000000..ebf68938e7
--- /dev/null
+++ b/test/validator/samples/logic-block-in-attribute/errors.json
@@ -0,0 +1,9 @@
+[
+	{
+		"code": "invalid-logic-block-placement",
+		"message": "{#if} logic block cannot be in attribute value",
+		"start": { "line": 1, "column": 12, "character": 12 },
+		"end": { "line": 1, "column": 12, "character": 12 },
+		"pos": 12
+	}
+]
diff --git a/test/validator/samples/logic-block-in-attribute/input.svelte b/test/validator/samples/logic-block-in-attribute/input.svelte
new file mode 100644
index 0000000000..241529527c
--- /dev/null
+++ b/test/validator/samples/logic-block-in-attribute/input.svelte
@@ -0,0 +1 @@
+<div style="{#if condition}a{/if}" />
\ No newline at end of file
diff --git a/test/validator/samples/logic-block-in-textarea/errors.json b/test/validator/samples/logic-block-in-textarea/errors.json
new file mode 100644
index 0000000000..b1d73d4903
--- /dev/null
+++ b/test/validator/samples/logic-block-in-textarea/errors.json
@@ -0,0 +1,9 @@
+[
+	{
+		"code": "invalid-logic-block-placement",
+		"message": "{#each} logic block cannot be inside <textarea>",
+		"start": { "line": 2, "column": 1, "character": 12 },
+		"end": { "line": 2, "column": 1, "character": 12 },
+		"pos": 12
+	}
+]
diff --git a/test/validator/samples/logic-block-in-textarea/input.svelte b/test/validator/samples/logic-block-in-textarea/input.svelte
new file mode 100644
index 0000000000..63fdd9fbaa
--- /dev/null
+++ b/test/validator/samples/logic-block-in-textarea/input.svelte
@@ -0,0 +1,5 @@
+<textarea>
+	{#each fruits as fruit}
+		{fruit}
+	{/each}
+</textarea>
\ No newline at end of file
diff --git a/test/validator/samples/security-anchor-rel-noreferrer/input.svelte b/test/validator/samples/security-anchor-rel-noreferrer/input.svelte
new file mode 100644
index 0000000000..de52d5a596
--- /dev/null
+++ b/test/validator/samples/security-anchor-rel-noreferrer/input.svelte
@@ -0,0 +1,31 @@
+<a href="https://svelte.dev" target="_blank">svelte website (invalid)</a>
+<a href="https://svelte.dev" target="_blank" rel="">svelte website (invalid)</a>
+<a href="https://svelte.dev" target="_blank" rel="noopener">svelte website (invalid)</a>
+<a href={'https://svelte.dev'} target="_blank">svelte website (invalid)</a>
+<a href={'https://svelte.dev'} target="_blank" rel="">svelte website (invalid)</a>
+<a href={'https://svelte.dev'} target="_blank" rel="noopener">svelte website (invalid)</a>
+<a href="//svelte.dev" target="_blank">svelte website (invalid)</a>
+<a href="//svelte.dev" target="_blank" rel="">svelte website (invalid)</a>
+<a href="//svelte.dev" target="_blank" rel="noopener">svelte website (invalid)</a>
+<a href="http://svelte.dev" target="_blank">svelte website (invalid)</a>
+<a href="http://svelte.dev" target="_blank" rel="">svelte website (invalid)</a>
+<a href="http://svelte.dev" target="_blank" rel="noopener">svelte website (invalid)</a>
+<a href="HTTP://svelte.dev" target="_blank">svelte website (invalid)</a>
+<a href="HTTP://svelte.dev" target="_blank" rel="">svelte website (invalid)</a>
+<a href="HTTP://svelte.dev" target="_blank" rel="noopener">svelte website (invalid)</a>
+<a href={'HTTPS://svelte.dev'} target="_blank">svelte website (invalid)</a>
+<a href={'HTTPS://svelte.dev'} target="_blank" rel="">svelte website (invalid)</a>
+<a href={'HTTPS://svelte.dev'} target="_blank" rel="noopener">svelte website (invalid)</a>
+<a href="same-host" target="_blank">Same host (valid)</a>
+<a href="same-host" target="_blank" rel="">Same host (valid)</a>
+<a href="same-host" target="_blank" rel="noopener">Same host (valid)</a>
+<a href="http://svelte.dev" target="_blank" rel="noreferrer">svelte website (valid)</a>
+<a href="http://svelte.dev" target="_blank" rel="noreferrer noopener">svelte website (valid)</a>
+<a href="HTTP://svelte.dev" target="_blank" rel="noreferrer">svelte website (valid)</a>
+<a href="HTTP://svelte.dev" target="_blank" rel="noreferrer noopener">svelte website (valid)</a>
+<a href="https://svelte.dev" target="_blank" rel="noreferrer">svelte website (valid)</a>
+<a href="https://svelte.dev" target="_blank" rel="noreferrer noopener">svelte website (valid)</a>
+<a href="HTTPS://svelte.dev" target="_blank" rel="noreferrer">svelte website (valid)</a>
+<a href="HTTPS://svelte.dev" target="_blank" rel="noreferrer noopener">svelte website (valid)</a>
+<a href="//svelte.dev" target="_blank" rel="noreferrer">svelte website (valid)</a>
+<a href="//svelte.dev" target="_blank" rel="noreferrer noopener">svelte website (valid)</a>
\ No newline at end of file
diff --git a/test/validator/samples/security-anchor-rel-noreferrer/warnings.json b/test/validator/samples/security-anchor-rel-noreferrer/warnings.json
new file mode 100644
index 0000000000..24c10fb763
--- /dev/null
+++ b/test/validator/samples/security-anchor-rel-noreferrer/warnings.json
@@ -0,0 +1,272 @@
+[
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 73,
+			"column": 73,
+			"line": 1
+		},
+		"pos": 0,
+		"start": {
+			"character": 0,
+			"column": 0,
+			"line": 1
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 154,
+			"column": 80,
+			"line": 2
+		},
+		"pos": 74,
+		"start": {
+			"character": 74,
+			"column": 0,
+			"line": 2
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 243,
+			"column": 88,
+			"line": 3
+		},
+		"pos": 155,
+		"start": {
+			"character": 155,
+			"column": 0,
+			"line": 3
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 319,
+			"column": 75,
+			"line": 4
+		},
+		"pos": 244,
+		"start": {
+			"character": 244,
+			"column": 0,
+			"line": 4
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 402,
+			"column": 82,
+			"line": 5
+		},
+		"pos": 320,
+		"start": {
+			"character": 320,
+			"column": 0,
+			"line": 5
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 493,
+			"column": 90,
+			"line": 6
+		},
+		"pos": 403,
+		"start": {
+			"character": 403,
+			"column": 0,
+			"line": 6
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 561,
+			"column": 67,
+			"line": 7
+		},
+		"pos": 494,
+		"start": {
+			"character": 494,
+			"column": 0,
+			"line": 7
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 636,
+			"column": 74,
+			"line": 8
+		},
+		"pos": 562,
+		"start": {
+			"character": 562,
+			"column": 0,
+			"line": 8
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 719,
+			"column": 82,
+			"line": 9
+		},
+		"pos": 637,
+		"start": {
+			"character": 637,
+			"column": 0,
+			"line": 9
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 792,
+			"column": 72,
+			"line": 10
+		},
+		"pos": 720,
+		"start": {
+			"character": 720,
+			"column": 0,
+			"line": 10
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 872,
+			"column": 79,
+			"line": 11
+		},
+		"pos": 793,
+		"start": {
+			"character": 793,
+			"column": 0,
+			"line": 11
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 960,
+			"column": 87,
+			"line": 12
+		},
+		"pos": 873,
+		"start": {
+			"character": 873,
+			"column": 0,
+			"line": 12
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 1033,
+			"column": 72,
+			"line": 13
+		},
+		"pos": 961,
+		"start": {
+			"character": 961,
+			"column": 0,
+			"line": 13
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 1113,
+			"column": 79,
+			"line": 14
+		},
+		"pos": 1034,
+		"start": {
+			"character": 1034,
+			"column": 0,
+			"line": 14
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 1201,
+			"column": 87,
+			"line": 15
+		},
+		"pos": 1114,
+		"start": {
+			"character": 1114,
+			"column": 0,
+			"line": 15
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 1277,
+			"column": 75,
+			"line": 16
+		},
+		"pos": 1202,
+		"start": {
+			"character": 1202,
+			"column": 0,
+			"line": 16
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 1360,
+			"column": 82,
+			"line": 17
+		},
+		"pos": 1278,
+		"start": {
+			"character": 1278,
+			"column": 0,
+			"line": 17
+		}
+	},
+	{
+		"code": "security-anchor-rel-noreferrer",
+		"message": "Security: Anchor with \"target=_blank\" should have rel attribute containing the value \"noreferrer\"",
+		"end": {
+			"character": 1451,
+			"column": 90,
+			"line": 18
+		},
+		"pos": 1361,
+		"start": {
+			"character": 1361,
+			"column": 0,
+			"line": 18
+		}
+	}
+]
diff --git a/test/validator/samples/style-directive-modifiers-invalid/errors.json b/test/validator/samples/style-directive-modifiers-invalid/errors.json
new file mode 100644
index 0000000000..245dfc63a8
--- /dev/null
+++ b/test/validator/samples/style-directive-modifiers-invalid/errors.json
@@ -0,0 +1,15 @@
+[{
+	"message": "Valid modifiers for style directives are: important",
+	"code": "invalid-style-directive-modifier",
+	"start": {
+		"line": 1,
+		"column": 8,
+		"character": 8
+	},
+	"end": {
+		"line": 1,
+		"column": 29,
+		"character": 29
+	},
+	"pos": 8
+}]
diff --git a/test/validator/samples/style-directive-modifiers-invalid/input.svelte b/test/validator/samples/style-directive-modifiers-invalid/input.svelte
new file mode 100644
index 0000000000..5fd7b1b1b5
--- /dev/null
+++ b/test/validator/samples/style-directive-modifiers-invalid/input.svelte
@@ -0,0 +1 @@
+<button style:color|bad='red'></button>
\ No newline at end of file