diff --git a/CHANGELOG.md b/CHANGELOG.md
index f4f648916f..53175a203c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## Unreleased
 
 * Allow multiple instances of the same action on an element ([#5516](https://github.com/sveltejs/svelte/pull/5516))
+* Support `foreign` namespace, which disables certain HTML5-specific behaviour and checks ([#5652](https://github.com/sveltejs/svelte/pull/5652))
 * Support inline comment sourcemaps in code from preprocessors ([#5854](https://github.com/sveltejs/svelte/pull/5854))
 
 ## 3.31.2
diff --git a/site/content/docs/02-template-syntax.md b/site/content/docs/02-template-syntax.md
index 6f1a2da61e..7288b8e8dd 100644
--- a/site/content/docs/02-template-syntax.md
+++ b/site/content/docs/02-template-syntax.md
@@ -1530,7 +1530,7 @@ The `<svelte:options>` element provides a place to specify per-component compile
 * `immutable={false}` — the default. Svelte will be more conservative about whether or not mutable objects have changed
 * `accessors={true}` — adds getters and setters for the component's props
 * `accessors={false}` — the default
-* `namespace="..."` — the namespace where this component will be used, most commonly "svg"
+* `namespace="..."` — the namespace where this component will be used, most commonly "svg"; use the "foreign" namespace to opt out of case-insensitive attribute names and HTML-specific warnings
 * `tag="..."` — the name to use when compiling this component as a custom element
 
 ```sv
diff --git a/site/content/docs/04-compile-time.md b/site/content/docs/04-compile-time.md
index 9fa0f92195..48f3ae2c4e 100644
--- a/site/content/docs/04-compile-time.md
+++ b/site/content/docs/04-compile-time.md
@@ -80,7 +80,7 @@ The following options can be passed to the compiler. None are required:
 | `outputFilename` | `null` | A `string` used for your JavaScript sourcemap.
 | `cssOutputFilename` | `null` | A `string` used for your CSS sourcemap.
 | `sveltePath` | `"svelte"` | The location of the `svelte` package. Any imports from `svelte` or `svelte/[module]` will be modified accordingly.
-
+| `namespace` | `"html"` | The namespace of the element; e.g., `"mathml"`, `"svg"`, `"foreign"`.
 
 ---
 
diff --git a/src/compiler/compile/Component.ts b/src/compiler/compile/Component.ts
index 5fb81e7457..d2b22c65e1 100644
--- a/src/compiler/compile/Component.ts
+++ b/src/compiler/compile/Component.ts
@@ -1349,7 +1349,8 @@ function process_component_options(component: Component, nodes) {
 			'accessors' in component.compile_options
 				? component.compile_options.accessors
 				: !!component.compile_options.customElement,
-		preserveWhitespace: !!component.compile_options.preserveWhitespace
+		preserveWhitespace: !!component.compile_options.preserveWhitespace,
+		namespace: component.compile_options.namespace
 	};
 
 	const node = nodes.find(node => node.name === 'svelte:options');
diff --git a/src/compiler/compile/index.ts b/src/compiler/compile/index.ts
index 842539fcde..9f9b31917e 100644
--- a/src/compiler/compile/index.ts
+++ b/src/compiler/compile/index.ts
@@ -6,6 +6,7 @@ import { CompileOptions, Warning } from '../interfaces';
 import Component from './Component';
 import fuzzymatch from '../utils/fuzzymatch';
 import get_name_from_filename from './utils/get_name_from_filename';
+import { valid_namespaces } from '../utils/namespaces';
 
 const valid_options = [
 	'format',
@@ -22,6 +23,7 @@ const valid_options = [
 	'hydratable',
 	'legacy',
 	'customElement',
+	'namespace',
 	'tag',
 	'css',
 	'loopGuardTimeout',
@@ -30,7 +32,7 @@ const valid_options = [
 ];
 
 function validate_options(options: CompileOptions, warnings: Warning[]) {
-	const { name, filename, loopGuardTimeout, dev } = options;
+	const { name, filename, loopGuardTimeout, dev, namespace } = options;
 
 	Object.keys(options).forEach(key => {
 		if (!valid_options.includes(key)) {
@@ -65,6 +67,15 @@ function validate_options(options: CompileOptions, warnings: Warning[]) {
 			toString: () => message
 		});
 	}
+
+	if (namespace && valid_namespaces.indexOf(namespace) === -1) {
+		const match = fuzzymatch(namespace, valid_namespaces);
+		if (match) {
+			throw new Error(`Invalid namespace '${namespace}' (did you mean '${match}'?)`);
+		} else {
+			throw new Error(`Invalid namespace '${namespace}'`);
+		}
+	}
 }
 
 export default function compile(source: string, options: CompileOptions = {}) {
diff --git a/src/compiler/compile/nodes/Element.ts b/src/compiler/compile/nodes/Element.ts
index b12e616f4d..8c5b4cb9f5 100644
--- a/src/compiler/compile/nodes/Element.ts
+++ b/src/compiler/compile/nodes/Element.ts
@@ -136,44 +136,45 @@ export default class Element extends Node {
 
 		this.namespace = get_namespace(parent as Element, this, component.namespace);
 
-		if (this.name === 'textarea') {
-			if (info.children.length > 0) {
-				const value_attribute = info.attributes.find(node => node.name === 'value');
-				if (value_attribute) {
-					component.error(value_attribute, {
-						code: 'textarea-duplicate-value',
-						message: 'A <textarea> can have either a value attribute or (equivalently) child content, but not both'
-					});
-				}
+		if (this.namespace !== namespaces.foreign) {
+			if (this.name === 'textarea') {
+				if (info.children.length > 0) {
+					const value_attribute = info.attributes.find(node => node.name === 'value');
+					if (value_attribute) {
+						component.error(value_attribute, {
+							code: 'textarea-duplicate-value',
+							message: 'A <textarea> can have either a value attribute or (equivalently) child content, but not both'
+						});
+					}
 
-				// this is an egregious hack, but it's the easiest way to get <textarea>
-				// children treated the same way as a value attribute
-				info.attributes.push({
-					type: 'Attribute',
-					name: 'value',
-					value: info.children
-				});
+					// this is an egregious hack, but it's the easiest way to get <textarea>
+					// children treated the same way as a value attribute
+					info.attributes.push({
+						type: 'Attribute',
+						name: 'value',
+						value: info.children
+					});
 
-				info.children = [];
+					info.children = [];
+				}
 			}
-		}
 
-		if (this.name === 'option') {
-			// Special case — treat these the same way:
-			//   <option>{foo}</option>
-			//   <option value={foo}>{foo}</option>
-			const value_attribute = info.attributes.find(attribute => attribute.name === 'value');
+			if (this.name === 'option') {
+				// Special case — treat these the same way:
+				//   <option>{foo}</option>
+				//   <option value={foo}>{foo}</option>
+				const value_attribute = info.attributes.find(attribute => attribute.name === 'value');
 
-			if (!value_attribute) {
-				info.attributes.push({
-					type: 'Attribute',
-					name: 'value',
-					value: info.children,
-					synthetic: true
-				});
+				if (!value_attribute) {
+					info.attributes.push({
+						type: 'Attribute',
+						name: 'value',
+						value: info.children,
+						synthetic: true
+					});
+				}
 			}
 		}
-
 		const has_let = info.attributes.some(node => node.type === 'Let');
 		if (has_let) {
 			scope = scope.child();
@@ -253,65 +254,83 @@ export default class Element extends Node {
 			});
 		}
 
-		if (a11y_distracting_elements.has(this.name)) {
-			// no-distracting-elements
-			this.component.warn(this, {
-				code: 'a11y-distracting-elements',
-				message: `A11y: Avoid <${this.name}> elements`
-			});
+		this.validate_attributes();
+		this.validate_event_handlers();
+		if (this.namespace === namespaces.foreign) {
+			this.validate_bindings_foreign();
+		} else {
+			this.validate_attributes_a11y();
+			this.validate_special_cases();
+			this.validate_bindings();
+			this.validate_content();
 		}
 
-		if (this.name === 'figcaption') {
-			let { parent } = this;
-			let is_figure_parent = false;
+	}
 
-			while (parent) {
-				if ((parent as Element).name === 'figure') {
-					is_figure_parent = true;
-					break;
-				}
-				if (parent.type === 'Element') {
-					break;
-				}
-				parent = parent.parent;
-			}
+	validate_attributes() {
+		const { component, parent } = this;
 
-			if (!is_figure_parent) {
-				this.component.warn(this, {
-					code: 'a11y-structure',
-					message: 'A11y: <figcaption> must be an immediate child of <figure>'
+		this.attributes.forEach(attribute => {
+			if (attribute.is_spread) return;
+
+			const name = attribute.name.toLowerCase();
+
+			// Errors
+
+			if (/(^[0-9-.])|[\^$@%&#?!|()[\]{}^*+~;]/.test(name)) {
+				component.error(attribute, {
+					code: 'illegal-attribute',
+					message: `'${name}' is not a valid attribute name`
 				});
 			}
-		}
 
-		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);
-				return true;
-			});
+			if (name === 'slot') {
+				if (!attribute.is_static) {
+					component.error(attribute, {
+						code: 'invalid-slot-attribute',
+						message: 'slot attribute cannot have a dynamic value'
+					});
+				}
 
-			const index = children.findIndex(child => (child as Element).name === 'figcaption');
+				if (component.slot_outlets.has(name)) {
+					component.error(attribute, {
+						code: 'duplicate-slot-attribute',
+						message: `Duplicate '${name}' slot`
+					});
 
-			if (index !== -1 && (index !== 0 && index !== children.length - 1)) {
-				this.component.warn(children[index], {
-					code: 'a11y-structure',
-					message: 'A11y: <figcaption> must be first or last child of <figure>'
-				});
+					component.slot_outlets.add(name);
+				}
+
+				if (!(parent.type === 'InlineComponent' || within_custom_element(parent))) {
+					component.error(attribute, {
+						code: 'invalid-slotted-content',
+						message: 'Element with a slot=\'...\' attribute must be a child of a component or a descendant of a custom element'
+					});
+				}
 			}
-		}
 
-		this.validate_attributes();
-		this.validate_special_cases();
-		this.validate_bindings();
-		this.validate_content();
-		this.validate_event_handlers();
-	}
+			// Warnings
 
-	validate_attributes() {
-		const { component, parent } = this;
+			if (this.namespace !== namespaces.foreign) {
+				if (name === 'is') {
+					component.warn(attribute, {
+						code: 'avoid-is',
+						message: 'The \'is\' attribute is not supported cross-browser and should be avoided'
+					});
+				}
 
-		const attribute_map = new Map();
+				if (react_attributes.has(attribute.name)) {
+					component.warn(attribute, {
+						code: 'invalid-html-attribute',
+						message: `'${attribute.name}' is not a valid HTML attribute. Did you mean '${react_attributes.get(attribute.name)}'?`
+					});
+				}
+			}
+		});
+	}
+
+	validate_attributes_a11y() {
+		const { component } = this;
 
 		this.attributes.forEach(attribute => {
 			if (attribute.is_spread) return;
@@ -408,60 +427,13 @@ export default class Element extends Node {
 					});
 				}
 			}
-
-
-			if (/(^[0-9-.])|[\^$@%&#?!|()[\]{}^*+~;]/.test(name)) {
-				component.error(attribute, {
-					code: 'illegal-attribute',
-					message: `'${name}' is not a valid attribute name`
-				});
-			}
-
-			if (name === 'slot') {
-				if (!attribute.is_static) {
-					component.error(attribute, {
-						code: 'invalid-slot-attribute',
-						message: 'slot attribute cannot have a dynamic value'
-					});
-				}
-
-				if (component.slot_outlets.has(name)) {
-					component.error(attribute, {
-						code: 'duplicate-slot-attribute',
-						message: `Duplicate '${name}' slot`
-					});
-
-					component.slot_outlets.add(name);
-				}
-
-				if (!(parent.type === 'InlineComponent' || within_custom_element(parent))) {
-					component.error(attribute, {
-						code: 'invalid-slotted-content',
-						message: 'Element with a slot=\'...\' attribute must be a child of a component or a descendant of a custom element'
-					});
-				}
-			}
-
-			if (name === 'is') {
-				component.warn(attribute, {
-					code: 'avoid-is',
-					message: 'The \'is\' attribute is not supported cross-browser and should be avoided'
-				});
-			}
-
-			if (react_attributes.has(attribute.name)) {
-				component.warn(attribute, {
-					code: 'invalid-html-attribute',
-					message: `'${attribute.name}' is not a valid HTML attribute. Did you mean '${react_attributes.get(attribute.name)}'?`
-				});
-			}
-
-			attribute_map.set(attribute.name, attribute);
 		});
 	}
 
+
 	validate_special_cases() {
 		const { component, attributes, handlers } = this;
+
 		const attribute_map = new Map();
 		const handlers_map = new Map();
 
@@ -576,6 +548,63 @@ export default class Element extends Node {
 				});
 			}
 		}
+
+		if (a11y_distracting_elements.has(this.name)) {
+			// no-distracting-elements
+			component.warn(this, {
+				code: 'a11y-distracting-elements',
+				message: `A11y: Avoid <${this.name}> elements`
+			});
+		}
+
+		if (this.name === 'figcaption') {
+			let { parent } = this;
+			let is_figure_parent = false;
+
+			while (parent) {
+				if ((parent as Element).name === 'figure') {
+					is_figure_parent = true;
+					break;
+				}
+				if (parent.type === 'Element') {
+					break;
+				}
+				parent = parent.parent;
+			}
+
+			if (!is_figure_parent) {
+				component.warn(this, {
+					code: 'a11y-structure',
+					message: 'A11y: <figcaption> must be an immediate child of <figure>'
+				});
+			}
+		}
+
+		if (this.name === 'figure') {
+			const children = this.children.filter(node => {
+				if (node.type === 'Comment') return false;
+				if (node.type === 'Text') return /\S/.test(node.data);
+				return true;
+			});
+
+			const index = children.findIndex(child => (child as Element).name === 'figcaption');
+
+			if (index !== -1 && (index !== 0 && index !== children.length - 1)) {
+				component.warn(children[index], {
+					code: 'a11y-structure',
+					message: 'A11y: <figcaption> must be first or last child of <figure>'
+				});
+			}
+		}
+	}
+
+	validate_bindings_foreign() {
+		this.bindings.forEach(binding => {
+			this.component.error(binding, {
+				code: 'invalid-binding',
+				message: `'${binding.name}' is not a valid binding. Foreign elements only support bind:this`
+			});
+		});
 	}
 
 	validate_bindings() {
diff --git a/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts b/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts
index 2969a7d82c..b9dbd0952d 100644
--- a/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts
+++ b/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts
@@ -8,6 +8,7 @@ import Expression from '../../../nodes/shared/Expression';
 import Text from '../../../nodes/Text';
 import handle_select_value_binding from './handle_select_value_binding';
 import { Identifier, Node } from 'estree';
+import { namespaces } from '../../../../utils/namespaces';
 
 export class BaseAttributeWrapper {
 	node: Attribute;
@@ -67,15 +68,26 @@ export default class AttributeWrapper extends BaseAttributeWrapper {
 			}
 		}
 
-		this.name = fix_attribute_casing(this.node.name);
-		this.metadata = this.get_metadata();
-		this.is_indirectly_bound_value = is_indirectly_bound_value(this);
-		this.property_name = this.is_indirectly_bound_value
-			? '__value'
-			: this.metadata && this.metadata.property_name;
+		if (this.parent.node.namespace == namespaces.foreign) {
+			// leave attribute case alone for elements in the "foreign" namespace
+			this.name = this.node.name;
+			this.metadata = this.get_metadata();
+			this.is_indirectly_bound_value = false;
+			this.property_name = null;
+			this.is_select_value_attribute = false;
+			this.is_input_value = false;
+		} else {
+			this.name = fix_attribute_casing(this.node.name);
+			this.metadata = this.get_metadata();
+			this.is_indirectly_bound_value = is_indirectly_bound_value(this);
+			this.property_name = this.is_indirectly_bound_value
+				? '__value'
+				: this.metadata && this.metadata.property_name;
+			this.is_select_value_attribute = this.name === 'value' && this.parent.node.name === 'select';
+			this.is_input_value = this.name === 'value' && this.parent.node.name === 'input';
+		}
+		
 		this.is_src = this.name === 'src'; // TODO retire this exception in favour of https://github.com/sveltejs/svelte/issues/3750
-		this.is_select_value_attribute = this.name === 'value' && this.parent.node.name === 'select';
-		this.is_input_value = this.name === 'value' && this.parent.node.name === 'input';
 		this.should_cache = should_cache(this);
 	}
 
diff --git a/src/compiler/interfaces.ts b/src/compiler/interfaces.ts
index 689b59529d..b9c95ae06d 100644
--- a/src/compiler/interfaces.ts
+++ b/src/compiler/interfaces.ts
@@ -124,6 +124,7 @@ export interface CompileOptions {
 	tag?: string;
 	css?: boolean;
 	loopGuardTimeout?: number;
+	namespace?: string;
 
 	preserveComments?: boolean;
 	preserveWhitespace?: boolean;
diff --git a/src/compiler/utils/namespaces.ts b/src/compiler/utils/namespaces.ts
index 3db7bc3fae..01d9bd60b3 100644
--- a/src/compiler/utils/namespaces.ts
+++ b/src/compiler/utils/namespaces.ts
@@ -1,3 +1,6 @@
+// The `foreign` namespace covers all DOM implementations that aren't HTML5.
+// It opts out of HTML5-specific a11y checks and case-insensitive attribute names.
+export const foreign = 'https://svelte.dev/docs#svelte_options';
 export const html = 'http://www.w3.org/1999/xhtml';
 export const mathml = 'http://www.w3.org/1998/Math/MathML';
 export const svg = 'http://www.w3.org/2000/svg';
@@ -6,12 +9,14 @@ export const xml = 'http://www.w3.org/XML/1998/namespace';
 export const xmlns = 'http://www.w3.org/2000/xmlns';
 
 export const valid_namespaces = [
+	'foreign',
 	'html',
 	'mathml',
 	'svg',
 	'xlink',
 	'xml',
 	'xmlns',
+	foreign,
 	html,
 	mathml,
 	svg,
@@ -20,4 +25,4 @@ export const valid_namespaces = [
 	xmlns
 ];
 
-export const namespaces: Record<string, string> = { html, mathml, svg, xlink, xml, xmlns };
+export const namespaces: Record<string, string> = { foreign, html, mathml, svg, xlink, xml, xmlns };
diff --git a/test/runtime/samples/attribute-casing-foreign-namespace-compiler-option/_config.js b/test/runtime/samples/attribute-casing-foreign-namespace-compiler-option/_config.js
new file mode 100644
index 0000000000..1225c64fc2
--- /dev/null
+++ b/test/runtime/samples/attribute-casing-foreign-namespace-compiler-option/_config.js
@@ -0,0 +1,20 @@
+// Test support for the `foreign` namespace preserving attribute case.
+
+export default {
+	html: `
+		<page horizontalAlignment="center">
+			<button textWrap="true" text="button">
+		</page>
+	`,
+	options: {
+		hydrate: false // Hydration test will fail as case sensitivity is only handled for svg elements.
+	},
+	compileOptions: {
+		namespace: 'foreign'
+	},
+	test({ assert, target }) {
+		const attr = sel => target.querySelector(sel).attributes[0].name;
+		assert.equal(attr('page'), 'horizontalAlignment');
+		assert.equal(attr('button'), 'textWrap');
+	}
+};
diff --git a/test/runtime/samples/attribute-casing-foreign-namespace-compiler-option/main.svelte b/test/runtime/samples/attribute-casing-foreign-namespace-compiler-option/main.svelte
new file mode 100644
index 0000000000..6300ab3b63
--- /dev/null
+++ b/test/runtime/samples/attribute-casing-foreign-namespace-compiler-option/main.svelte
@@ -0,0 +1,3 @@
+<page horizontalAlignment="center">
+	<button textWrap="true" text="button">
+</page>
\ No newline at end of file
diff --git a/test/runtime/samples/attribute-casing-foreign-namespace/_config.js b/test/runtime/samples/attribute-casing-foreign-namespace/_config.js
new file mode 100644
index 0000000000..d7eca6aba9
--- /dev/null
+++ b/test/runtime/samples/attribute-casing-foreign-namespace/_config.js
@@ -0,0 +1,18 @@
+// Test support for the `foreign` namespace preserving attribute case.
+
+export default {
+	html: `
+		<page horizontalAlignment="center">
+			<button textWrap="true" text="button">
+		</page>
+	`,
+	options: {
+		hydrate: false // Hydration test will fail as case sensitivity is only handled for svg elements.
+	},
+
+	test({ assert, target }) {
+		const attr = sel => target.querySelector(sel).attributes[0].name;
+		assert.equal(attr('page'), 'horizontalAlignment');
+		assert.equal(attr('button'), 'textWrap');
+	}
+};
diff --git a/test/runtime/samples/attribute-casing-foreign-namespace/main.svelte b/test/runtime/samples/attribute-casing-foreign-namespace/main.svelte
new file mode 100644
index 0000000000..f5ff10a3eb
--- /dev/null
+++ b/test/runtime/samples/attribute-casing-foreign-namespace/main.svelte
@@ -0,0 +1,4 @@
+<svelte:options namespace="foreign" />
+<page horizontalAlignment="center">
+	<button textWrap="true" text="button">
+</page>
\ No newline at end of file
diff --git a/test/validator/index.ts b/test/validator/index.ts
index 1709b7a706..72364ea89a 100644
--- a/test/validator/index.ts
+++ b/test/validator/index.ts
@@ -101,4 +101,22 @@ describe('validate', () => {
 
 		assert.deepEqual(warnings, []);
 	});
+
+	it('errors if namespace is provided but unrecognised', () => {
+		assert.throws(() => {
+			svelte.compile('<div></div>', {
+				name: 'test',
+				namespace: 'svefefe'
+			});
+		}, /Invalid namespace 'svefefe'/);
+	});
+
+	it('errors with a hint if namespace is provided but unrecognised but close', () => {
+		assert.throws(() => {
+			svelte.compile('<div></div>', {
+				name: 'test',
+				namespace: 'foriegn'
+			});
+		}, /Invalid namespace 'foriegn' \(did you mean 'foreign'\?\)/);
+	});
 });
diff --git a/test/validator/samples/a11y-in-foreign-namespace/input.svelte b/test/validator/samples/a11y-in-foreign-namespace/input.svelte
new file mode 100644
index 0000000000..aeef580c73
--- /dev/null
+++ b/test/validator/samples/a11y-in-foreign-namespace/input.svelte
@@ -0,0 +1,7 @@
+<svelte:options namespace="foreign" />
+<page>
+    <a>not actually a link</a>
+    <label>This isn't a html label</label>
+    <figure>This is maybe a QT figure</figure>
+</page>
+
diff --git a/test/validator/samples/a11y-in-foreign-namespace/warnings.json b/test/validator/samples/a11y-in-foreign-namespace/warnings.json
new file mode 100644
index 0000000000..fe51488c70
--- /dev/null
+++ b/test/validator/samples/a11y-in-foreign-namespace/warnings.json
@@ -0,0 +1 @@
+[]
diff --git a/test/validator/samples/binding-invalid-foreign-namespace/errors.json b/test/validator/samples/binding-invalid-foreign-namespace/errors.json
new file mode 100644
index 0000000000..c726270266
--- /dev/null
+++ b/test/validator/samples/binding-invalid-foreign-namespace/errors.json
@@ -0,0 +1,15 @@
+[{
+	"code": "invalid-binding",
+	"message": "'value' is not a valid binding. Foreign elements only support bind:this",
+	"pos": 81,
+	"start": {
+		"line": 6,
+		"column": 7,
+		"character": 81
+	},
+	"end": {
+		"line": 6,
+		"column": 28,
+		"character": 102
+	}
+}]
diff --git a/test/validator/samples/binding-invalid-foreign-namespace/input.svelte b/test/validator/samples/binding-invalid-foreign-namespace/input.svelte
new file mode 100644
index 0000000000..e40f44e906
--- /dev/null
+++ b/test/validator/samples/binding-invalid-foreign-namespace/input.svelte
@@ -0,0 +1,6 @@
+<svelte:options namespace="foreign" />
+<script>
+	let whatever;
+</script>
+
+<input bind:value={whatever} />