add some more CE docs

site/content/docs/03-run-time.md

@@ -934,6 +934,18 @@ customElements.define('my-element', MyElement);
 
 ---
 
+Once a custom element has been defined, it can be used as a regular DOM element:
+
+```js
+document.body.innerHTML = `
+	<my-element>
+		<p>This is some slotted content</p>
+	</my-element>
+`;
+```
+
+---
+
 By default, custom elements are compiled with `accessors: true`, which means that any [props](docs#Attributes_and_props) are exposed as properties of the DOM element (as well as being readable/writable as attributes, where possible).
 
 To prevent this, add `accessors={false}` to `<svelte:options>`.
@@ -953,6 +965,8 @@ Custom elements can be a useful way to package components for consumption in a n
 * Styles are *encapsulated*, rather than merely *scoped*. This means that any non-component styles (such as you might have in a `global.css` file) will not apply to the custom element, including styles with the `:global(...)` modifier
 * Instead of being extracted out as a separate .css file, styles are inlined into the component as a JavaScript string
 * Custom elements are not generally suitable for server-side rendering, as the shadow DOM is invisible until JavaScript loads
+* In Svelte, slotted content renders *lazily*. In the DOM, it renders *eagerly*. In other words, it will always be created even if the component's `<slot>` element is inside an `{#if ...}` block. Similarly, including a `<slot>` in an `{#each ...}` block will not cause the slotted content to be rendered multiple times
+* The `let:` directive has no effect
 * Polyfills are required to support older browsers