Components can have child content, in the same way that elements can.
The content is exposed in the child component using the `<slot>` element, which can contain fallback content that is rendered if no children are provided.
```svelte
<!-- Widget.svelte -->
<div>
<slot>
this fallback content will be rendered when no content is provided, like in the first example
</slot>
</div>
<!-- App.svelte -->
<Widget/>
<!-- this component will render the default content -->
<Widget>
<p>this is some child content that will overwrite the default slot content</p>
</Widget>
```
Note: If you want to render regular `<slot>` element, You can use `<svelte:element this="slot" />`.
### `<slot name="`_name_`">`
Named slots allow consumers to target specific areas. They can also have fallback content.
Components can be placed in a named slot using the syntax `<Component slot="name" />`.
In order to place content in a slot without using a wrapper element, you can use the special element `<svelte:fragment>`.
```svelte
<!-- Widget.svelte -->
<div>
<slotname="header">No header was provided</slot>
<p>Some content between header and footer</p>
<slotname="footer"/>
</div>
<!-- App.svelte -->
<Widget>
<HeaderComponentslot="header"/>
<svelte:fragmentslot="footer">
<p>All rights reserved.</p>
<p>Copyright (c) 2019 Svelte Industries</p>
</svelte:fragment>
</Widget>
```
### $$slots
`$$slots` is an object whose keys are the names of the slots passed into the component by the parent. If the parent does not pass in a slot with a particular name, that name will not be present in `$$slots`. This allows components to render a slot (and other elements, like wrappers for styling) only if the parent provides it.
Note that explicitly passing in an empty named slot will add that slot's name to `$$slots`. For example, if a parent passes `<div slot="title" />` to a child component, `$$slots.title` will be truthy within the child.
```svelte
<!-- Card.svelte -->
<div>
<slotname="title"/>
{#if $$slots.description}
<!-- This <hr> and slot will render only if a slot named "description" is provided. -->
<hr/>
<slotname="description"/>
{/if}
</div>
<!-- App.svelte -->
<Card>
<h1slot="title">Blog Post Title</h1>
<!-- No slot named "description" was provided so the optional slot will not be rendered. -->
</Card>
```
### `<slot key={`_value_`}>`
Slots can be rendered zero or more times and can pass values _back_ to the parent using props. The parent exposes the values to the slot template using the `let:` directive.
The usual shorthand rules apply — `let:item` is equivalent to `let:item={item}`, and `<slot {item}>` is equivalent to `<slot item={item}>`.
```svelte
<!-- FancyList.svelte -->
<ul>
{#each items as item}
<liclass="fancy">
<slotprop={item}/>
</li>
{/each}
</ul>
<!-- App.svelte -->
<FancyList{items}let:prop={thing}>
<div>{thing.text}</div>
</FancyList>
```
Named slots can also expose values. The `let:` directive goes on the element with the `slot` attribute.
The `<svelte:component>` element renders a component dynamically, using the component constructor specified as the `this` property. When the property changes, the component is destroyed and recreated.
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) do not work with a dynamic tag type.
If `this` has a nullish value, the element and its children will not be rendered.
If `this` is the name of a [void element](https://developer.mozilla.org/en-US/docs/Glossary/Void_element) (e.g., `br`) and `<svelte:element>` has child elements, a runtime error will be thrown in development mode.
The `<svelte:window>` element allows you to add event listeners to the `window` object without worrying about removing them when the component is destroyed, or checking for the existence of `window` when server-side rendering.
Unlike `<svelte:self>`, this element may only appear at the top level of your component and must never be inside a block or element.
> Note that the page will not be scrolled to the initial value to avoid accessibility issues. Only subsequent changes to the bound variable of `scrollX` and `scrollY` will cause scrolling. However, if the scrolling behaviour is desired, call `scrollTo()` in `onMount()`.
Similarly to `<svelte:window>`, this element allows you to add listeners to events on `document`, such as `visibilitychange`, which don't fire on `window`. It also lets you use [actions](/docs/element-directives#use-action) on `document`.
As with `<svelte:window>`, this element may only appear the top level of your component and must never be inside a block or element.
Similarly to `<svelte:window>`, this element allows you to add listeners to events on `document.body`, such as `mouseenter` and `mouseleave`, which don't fire on `window`. It also lets you use [actions](/docs/element-directives#use-action) on the `<body>` element.
As with `<svelte:window>` and `<svelte:document>`, this element may only appear the top level of your component and must never be inside a block or element.
This element makes it possible to insert elements into `document.head`. During server-side rendering, `head` content is exposed separately to the main `html` content.
As with `<svelte:window>`, `<svelte:document>` and `<svelte:body>`, this element may only appear at the top level of your component and must never be inside a block or element.
The `<svelte:options>` element provides a place to specify per-component compiler options, which are detailed in the [compiler section](/docs/svelte-compiler#compile). The possible options are:
-`immutable={true}` — you never use mutable data, so the compiler can do simple referential equality checks to determine if values have changed
-`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"; use the "foreign" namespace to opt out of case-insensitive attribute names and HTML-specific warnings
The `<svelte:fragment>` element allows you to place content in a [named slot](/docs/special-elements#slot-slot-name-name) without wrapping it in a container DOM element. This keeps the flow layout of your document intact.
