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<!DOCTYPE html>
<html>
<head>
<meta charset='utf-8'/>
<title>Shadow DOM</title>
<script src='./autolink-config.js' class='remove'></script>
<script src='../../assets/scripts/autolink.js' class='remove'></script>
<link rel="stylesheet" href="../../assets/styles/respec-complement.css" type="text/css" />
<script src='//www.w3.org/Tools/respec/respec-w3c-common' async class='remove'></script>
<script class='remove'>
var respecConfig = {
specStatus: "ED",
shortName: "shadow-dom",
editors: [{ name: "Dimitri Glazkov", url: "mailto:dglazkov@chromium.org", company: "Google, Inc." },
{ name: "Hayato Ito", url: "mailto:hayato@google.com", company: "Google, Inc." }],
wg: "W3C Web Applications (WebApps)",
wgURI: "http://www.w3.org/2008/webapps/",
wgPublicList: "public-webapps",
wgPatentURI: "",
edDraftURI: "http://w3c.github.io/webcomponents/spec/shadow/",
otherLinks: [
{
key: "Revision history",
href: "https://github.com/w3c/webcomponents/commits/gh-pages/spec/shadow/"
}
],
localBiblio: {
"SELECTORS4": {
title: "Selectors Level 4",
href: "http://dev.w3.org/csswg/selectors4/",
authors: ["Elika Etemad", "Tab Atkins Jr"],
status: "ED"
},
"DOMPARSING": {
title: "DOM Parsing and Serialization",
href: "http://domparsing.spec.whatwg.org/",
authors: ["Ms2ger"]
},
"EDITING": {
title: "HTML Editing APIs",
href: "https://dvcs.w3.org/hg/editing/raw-file/tip/editing.html",
authors: ["Aryeh Gregor"]
}
}
};
var bugAssistConfig = {
blocked: '14978',
short_desc: '[Shadow]: ',
product: 'WebAppsWG',
component: 'Component Model'
};
</script>
<script src="../../assets/scripts/bug-assist.js" class="remove"></script>
</head>
<body>
<section id='abstract'>
<p>
This specification describes a method of combining multiple DOM trees into one hierarchy and how these trees interact with each other within a document, thus
enabling better composition of the DOM.
</p>
</section>
<section id='sotd'>
</section>
<section>
<h2>Conformance</h2>
<p>All diagrams, examples, notes, are non-normative, as well as sections explicitly marked as non-normative. Everything else in this specification is normative.</p>
<p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in [[!RFC2119]]. For readability, these words do not appear in all uppercase letters in this specification.</p>
<p>To help with layering and to avoid circular dependencies between various parts of specification, this document consists of three consecutive narratives:</p>
<ol>
<li>setting up the stage for the specification,</li>
<li>explaining of the conceptual model and algorithms behind it, and</li>
<li>expressing this model with DOM interfaces and HTML elements.</li>
</ol>
<p>In a sense, these parts can be viewed as <em>math</em>, which sets up the reasoning environment, <em>physics</em>, which is the theoretical reasoning about the concept, and <em>mechanics</em>, which is the practical application of this reasoning.</p>
<p>Any point, at which a conforming UA must make decisions about the state or reaction to the state of the conceptual model, is captured as <a href="http://en.wikipedia.org/wiki/Algorithm">algorithm</a>. The algorithms are defined in terms of processing equivalence. The <dfn>processing equivalence</dfn> is a constraint imposed on the algorithm implementors, requiring the output of the both UA-implemented and the specified algorithm to be exactly the same for all inputs.</p>
</section>
<section>
<h2>Concepts</h2>
<section class="informative">
<h3>Introduction</h3>
<p>
See the <a href="http://www.html5rocks.com/en/tutorials/webcomponents/shadowdom/">Shadow DOM 101</a> as a non-normative introduction.
</p>
</section>
<section>
<h3>Shadow trees</h3>
<p>A <dfn>document tree</dfn> is a <a>node tree</a> [[!DOM]] whose <a>root</a> <a>node</a> is a <a>document</a>.</p>
<p>Any element can have an <dfn title="shadow roots list">associated ordered list</dfn> of zero or more <a title="node tree">node trees</a>.</p>
<p>An element <dfn>hosts</dfn> a <a>node tree</a> if the <a>node tree</a> is a member of this associated list.</p>
<p>A <dfn>shadow host</dfn> is an element that <a>hosts</a> one or more <a title="node tree">node trees</a>.</p>
<p>A <dfn>shadow tree</dfn> is a <a>node tree</a> <a title="hosts">hosted</a> by a <a>shadow host</a>.</p>
<p>A <dfn>shadow root</dfn> is the <a>root</a> <a>node</a> of a shadow tree.</p>
<p>If more than one <a>shadow tree</a> is <a title="hosts">hosted</a> by the same <a>shadow host</a>, the more recently added <a>shadow tree</a> is called the <dfn>younger shadow tree</dfn> and the less recently added <a>shadow tree</a> is called the <dfn>older shadow tree</dfn>.</p>
<p>If there is no <a>older shadow tree</a> than a given <a>shadow tree</a>,
the <a>shadow tree</a> is called the <dfn>oldest shadow tree</dfn>.</p>
<p>If there is no <a>younger shadow tree</a> than a given <a>shadow tree</a>,
the <a>shadow tree</a> is called the <dfn>youngest shadow tree</dfn>.</p>
<p>The <dfn>older shadow root</dfn> is the root node of the <a>older shadow tree</a>.</p>
<p>The <dfn>younger shadow root</dfn> is the root node of the <a>younger shadow tree</a>.</p>
<p>The <dfn>oldest shadow root</dfn> is the root node of the <a>oldest shadow tree</a>.</p>
<p>The <dfn>youngest shadow root</dfn> is the root node of the <a>youngest shadow tree</a>.</p>
<p>
A node <var>A</var> is called a <dfn>child or hosted shadow root</dfn> of a node <var>B</var>,
if either <var>A</var> is a child of <var>B</var> or A is the <a>root</a> node of the <a>shadow tree</a> that B <a>hosts</a>.
</p>
<p>
A node <var>A</var> is called a <dfn>deep descendant</dfn> of a node <var>B</var>,
if either <var>A</var> is a <a>child or hosted shadow root</a> of <var>B</var>
or <var>A</var> is <a>child or hosted shadow root</a> of a node <var>C</var> that is a <a>deep descendant</a> of <var>B</var>.
</p>
<p>
An <dfn>inclusive deep descendant</dfn> is a node or one of its <a title="deep descendant">deep descendants</a>.
</p>
<p>
When an element is an <a>inclusive deep descendant</a> of a <a>document element</a>, it is <dfn>in a document deeply</dfn>.
</p>
</section>
<section>
<h3>Trees of trees</h3>
<p>A <dfn>tree of trees</dfn> is a <a>tree</a> of <a title="node tree">node trees</a>.</p>
<p class="note">
The purpose of introducing a tree of trees here is to define algorithms easily in the following sections.
This is a kind of a notation techchique to make the this specification simpler.
</p>
<p>Just like a <a>node tree</a> is defined as <a title="tree">a set of relationships</a> between <a title="node">nodes</a>,
a <a>tree of trees</a> is similarly defined as a set of relationships between <a title="node tree">node trees</a>:</p>
<ul>
<li>
A <a>node tree</a> <var>A</var> is called a <dfn>parent tree</dfn> of a <a>node tree</a> <var>B</var> if either of the following conditions is satisfied:
<ul>
<li><var>A</var> and <var>B</var> are next to each other in the same <a title="shadow roots list">associated ordered list</a> and <var>A</var> is the <a>older shadow tree</a> relative to <var>B</var>.</li>
<li><var>B</var> is the <a>oldest shadow tree</a> and <a>shadow host</a> of <var>B</var> participates in <var>A</var>.</li>
</ul>
</li>
<li>If there is more than one <a>node tree</a> that shares the same <a>parent tree</a>, the <a>tree order</a> between them in the <a>tree of trees</a> is defined as follows:
<ol>
<li>Let <var>A</var> and <var>B</var> be <a title="node tree">node trees</a> that share the same <a>parent tree</a>.</li>
<li><var>A</var> comes before <var>B</var> if either of the following conditions is satisfied:
<ul>
<li>The <a>shadow host</a> which <a>hosts</a> <var>A</var> is <a>preceding</a> the <a>shadow host</a> which <a>hosts</a> <var>B</var>.</li>
<li><var>B</var> is not the <a>oldest shadow tree</a>.</li>
</ul>
</li>
</ol>
</li>
<li>Other relationships and terms, such as <dfn>root tree</dfn>, <dfn>child tree</dfn>,
<dfn>descendant tree</dfn>, <dfn>inclusive descendant tree</dfn>,
<dfn>ancestor tree</dfn>, <dfn>inclusive ancestor tree</dfn>,
<dfn>preceding tree</dfn>
are defined in the similar way as defined in <a title="tree">trees</a>.</li>
</ul>
<p>The <a><code>ownerDocument</code></a> property of a <a>node</a> in a shadow tree <strong>must</strong> refers to the <a>document</a> of the <a>shadow host</a> which <a>hosts</a> the shadow tree.</p>
<p><a><code>Window</code></a> object <a title="named access on the window object">named properties</a> [[!HTML]] <strong>must</strong> access the <a title="node">nodes</a> in the <a>document tree</a>.</p>
<section class="informative">
<h3>Example tree of trees</h3>
<figure>
<object data="../../assets/images/tree-of-trees.svg" width="650" height="823"></object>
<figcaption>
A tree of trees.
</figcaption>
</figure>
<p>
In the figure, there are six node trees, named A, B, C, D, E and F.
The node trees, C, D and E, are hosted by the same <a>shadow host</a>, which participates in the node tree A.
The node tree C is the <a>oldest shadow tree</a>. The node tree E is the <a>youngest shadow tree</a>.
The following set of relationships holds in the figure:
<ul>
<li>The ordered list of A's <a title="child tree">child trees</a> is [B, C].</li>
<li>The ordered list of B's <a title="child tree">child trees</a> is [].</li>
<li>The ordered list of C's <a title="child tree">child trees</a> is [F, D].</li>
<li>The ordered list of D's <a title="child tree">child trees</a> is [E].</li>
<li>The ordered list of E's <a title="child tree">child trees</a> is [].</li>
</ul>
</p>
</section>
</section>
<section>
<h3>Composed trees</h3>
<p>A <dfn>composed tree</dfn> is a <a>node tree</a> which is constructed out of <a title="node">nodes</a> from multiple <a title="node tree">node trees</a> in a <a>tree of trees</a>.
The exact algorithm of constructing a composed tree is specified later.</p>
<figure>
<object data="../../assets/images/composed-tree.svg" width="654" height="606"></object>
<figcaption>A composed tree</figcaption>
</figure>
<p>
If an element doesn't <a>participate</a> in a <a>composed tree</a> whose <a>root</a> node is a document, the element <strong>must</strong> not appear in the <a>formating structure</a> [[!CSS21]] nor create any CSS <a>box</a>.
This behavior <strong>must</strong> not be overridden by setting the 'display' property.
</p>
<p>
In resolving CSS <a>inheritance</a>, an element <strong>must</strong> inherit from the parent node in the <a>composed tree</a>, if applicable.
</p>
</section>
</section>
<section>
<h2>Distributions</h2>
<section>
<h3>Insertion Points</h3>
<p>An <dfn>insertion point</dfn> is a defined location where <a title="node">nodes</a> in a different <a>node tree</a> appear instead of the nodes's original position when constructing a <a>composed tree</a>.</p>
<figure>
<object data="../../assets/images/distributions.svg" width="663" height="598"></object>
<figcaption>A distribution</figcaption>
</figure>
<p>A <dfn>distribution</dfn> is the mechanism that determines which <a title="node">nodes</a> appear at each <a>insertion point</a>. The exact algorithm of a <a>distribution</a> is specified later.</p>
</section>
<section>
<h3>Content Insertion Points</h3>
<p>A <dfn>content insertion point</dfn> is an <a>insertion point</a> to where the child <a title="node">nodes</a> of the <a>shadow host</a> are distributed.
The <a>content element</a> that satisfies all of the following conditions represents a <a>content insertion point</a>:</p>
<ul>
<li>The <a>root</a> <a>node</a> of the <a>content element</a> is a <a>shadow root</a></li>
<li>There is no other <a>content element</a> in the <a title="ancestor">ancestors</a> of the <a>content element</a></li>
<li>There is no <a>shadow element</a> in the <a title="ancestor">ancestors</a> of the <a>content element</a></li>
</ul>
</section>
<section>
<h3>Shadow Insertion Points</h3>
<p>A <dfn>shadow insertion point</dfn> is an <a>insertion point</a> to where the children of the <a>older shadow root</a> are distributed.
The <a>shadow element</a> that satisfies of the following conditions represents a <a>shadow insertion point</a>:</p>
<ul>
<li>The <a>root</a> <a>node</a> of the <a>shadow element</a> is a <a>shadow root</a></li>
<li>There is no other <a>shadow element</a> which is <a>preceding</a> the <a>shadow element</a></li>
<li>There is no other <a>content element</a> in the <a title="ancestor">ancestors</a> of the <a>shadow element</a></li>
</ul>
</section>
<section>
<h3>Distribution Results</h3>
<p>Each <a>tree of trees</a> has the <dfn>distribution result</dfn> which describes the result of distributions.
The <a>distribution result</a> <strong>must</strong> be <a title="processing equivalence">equivalent</a> of the following:</p>
<ol>
<li>Each <a>insertion point</a> has an ordered list, called <dfn>distributed nodes</dfn>, which consists of <a title="node">nodes</a> which are distributed into the <a>insertion point</a>.</li>
<li>Each <a>node</a> that is not an <a>insertion point</a> has an ordered list, called <dfn>destination insertion points</dfn>, which consists of <a title="insertion point">insertion points</a> to where the <a>node</a> is distributed</li>
</ol>
<p>An <a>insertion point</a> <var>A</var> is the <dfn>final destination</dfn> of a <a>node</a> <var>B</var> if <var>A</var> is the last item of the <a>destination insertion points</a> of <var>B</var>.</p>
<p>When a <a>node</a> <var>A</var> is <dfn title="distributes">distributed</dfn> into an <a>insertion point</a> <var>B</var>, the following steps <strong>must</strong> happen:</p>
<ul>
<li>Add <var>A</var> to the <a>distributed nodes</a> of <var>B</var></li>
<li>Add <var>B</var> to the <a>destination insertion points</a> of <var>A</var></li>
</ul>
<div class="note">
<p>One case that deserves special consideration is the situation when an <a>insertion point</a> is a child <a>node</a> of another <a>shadow host</a>. In such situations, the <a title="node">nodes</a> <a title="distributes">distributed</a> into that <a>insertion point</a> appear as if they were child <a title="node">nodes</a> of the <a>shadow host</a> in the context of <a>distribution</a>. Thus, the <a title="node">nodes</a> <a title="distributes">distributed</a> to a <a>shadow tree</a> could have already been <a title="distributes">distributed</a> from its parent tree.</p>
<p>Despite being distributed to more than one insertion point, a node still only appears once in the composed tree at the final destination.</p>
</div>
<figure>
<object data="../../assets/images/re-distributions.svg" width="693" height="822"></object>
<figcaption>A re-distribution.
In the figure, a node <em>child 1</em> is distributed into <em>insertion point 1</em>. Then <em>child1</em> is re-distributed into <em>insertion point 3</em>.
The destination insertion points of <em>child 1</em> is [<em>insertion point 1</em>, <em>insertion point 3</em>] and <em>insertion point 3</em> is the final destination of <em>child 1</em>.
The distributed nodes of <em>insertion point 1</em> and <em>insertion point 3</em> is [<em>child 1</em>] and [<em>child 1</em>, <em>child 3</em>], respectively.
</figcaption>
</figure>
</section>
<section>
<h3>Distribution Algorithms</h3>
<p>The <dfn>distribution algorithm</dfn> <strong>must</strong> be used to determine the <a>distribution result</a> for a <a>tree of trees</a> and <strong>must</strong> be <a title="processing equivalence">equivalent</a> to processing the following steps:</p>
<div class="algorithm">
<dl>
<dt>Input</dt>
<dd><var>TREE-OF-TREES</var>, a <a>tree of trees</a></dd>
<dt>Output</dt>
<dd>The <a>distribution result</a> of <var>TREE-OF-TREES</var> is updated</dd>
</dl>
<ol>
<li>Let all <a>distributed nodes</a> and <a>destination insertion points</a> owned by <a title="node">nodes</a> in <var>TREE-OF-TREES</var> be empty</li>
<li>Let <var>ROOT-TREE</var> be the <a>root tree</a> of <var>TREE-OF-TREES</var></li>
<li>Run the <a>distribution resolution algorithm</a> with <var>ROOT-TREE</var> as input</li>
</ol>
</div>
<p>The <dfn>distribution resolution algorithm</dfn> <strong>must</strong> be used to determine the <a>distribution result</a> for a given <a>node tree</a> and its <a title="descendant tree">descendant trees</a>, and <strong>must</strong> be <a title="processing equivalence">equivalent</a> to processing the following steps:</p>
<div class="algorithm">
<dl>
<dt>Input</dt>
<dd><var>NODE-TREE</var>, a <a>node tree</a></dd>
<dt>Output</dt>
<dd>The <a>distribution result</a> is updated for the <a title="inclusive descendant tree">inclusive descendant trees</a> of <var>NODE-TREE</var></dd>
</dl>
<ol>
<li>For each <a>shadow host</a>, <var>SHADOW-HOST</var>, which participates in <var>NODE-TREE</var>, in <a>tree order</a>:
<ol>
<li>Let <var>POOL</var> be the result of the <a>pool population algorithm</a> with <var>SHADOW-HOST</var> as input</li>
<li>For each <a>shadow tree</a>, <var>SHADOW-TREE</var>, which <var>SHADOW-HOST</var> <a>hosts</a>, in order from the <a>youngest shadow tree</a> to the <a>oldest shadow tree</a>:
<ol>
<li>Run the <a>pool distribution algorithm</a> with <var>SHADOW-TREE</var> and <var>POOL</var> as input</li>
</ol></li>
<li>For each <a>shadow tree</a>, <var>SHADOW-TREE</var>, that <var>SHADOW-HOST</var> <a>hosts</a>, in order from the <a>oldest shadow tree</a> to the <a>youngest shadow tree</a>:
<ol>
<li>Let <var>SHADOW</var> be the <a>shadow insertion point</a> which participates in <var>SHADOW-TREE</var></li>
<li>If such a <var>SHADOW</var> exits:
<ol>
<li>If <var>SHADOW-TREE</var> is not the <a>oldest shadow tree</a>:
<ol>
<li>Let <var>POOL</var> be the result of the <a>pool population algorithm</a> with the root node of the <a>older shadow tree</a> relative to <var>SHADOW-TREE</var> as input.</li>
</ol></li>
<li>For each <a>node</a>, <var>CHILD</var>, in <var>POOL</var>
<ol>
<li><a title="distributes">Distribute</a> <var>CHILD</var> into <var>SHADOW</var></li>
</ol></li>
</ol></li>
<li>Run the <a>distribution resolution algorithm</a>, recursively, with <var>SHADOW-TREE</var> as input</li>
</ol></li>
</ol></li>
</ol>
</div>
<p>The <dfn>pool population algorithm</dfn> <strong>must</strong> be used to populate <a title="node">nodes</a> from the child <a title="node">nodes</a> of a given <a>node</a> and <strong>must</strong> be <a title="processing equivalence">equivalent</a> to processing the following steps:</p>
<div class="algorithm">
<dl>
<dt>Input</dt>
<dd><var>NODE</var>, a node</dd>
<dt>Output</dt>
<dd><var>POOL</var>, an ordered list of nodes</dd>
</dl>
<ol>
<li>Let <var>POOL</var> be an empty ordered list.</li>
<li>For each child <a>node</a>, <var>CHILD</var>, of <var>NODE</var>:
<ol>
<li>If <var>CHILD</var> is an <a>insertion point</a>:
<ol>
<li>Add all <a title="node">nodes</a> in the <a>distributed nodes</a> of <var>CHILD</var> to <var>POOL</var></li>
</ol></li>
<li>Otherwise:
<ol>
<li>Add <var>CHILD</var> to <var>POOL</var></li>
</ol></li>
</ol></li>
</ol>
</div>
<p>The <dfn>pool distribution algorithm</dfn> <strong>must</strong> be used to distribute <a title="node">nodes</a> in a pool into the <a title="content insertion point">content insertion points</a> in a <a>shadow tree</a> and <strong>must</strong> be <a title="processing equivalence">equivalent</a> to processing the following steps:</p>
<div class="algorithm">
<dl>
<dt>Input</dt>
<dd><var>SHADOW-TREE</var>, a shadow tree</dd>
<dd><var>POOL</var>, an ordered list of nodes</dd>
<dt>Output</dt>
<dd>Nodes in POOL are distributed into the content insertion points in the tree.</dd>
</dl>
<ol>
<li>For each <a>content insertion point</a>, <var>CONTENT</var>, which participates in <var>SHADOW-TREE</var>, in tree order:
<ol>
<li>For each <a>node</a>, <var>NODE</var>, in <var>POOL</var>
<ol>
<li>If <var>NODE</var> satisfies <var>CONTENT</var>'s matching criteria:
<ol>
<li><a title="distributes">Distribute</a> <var>NODE</var> into <var>CONTENT</var></li>
<li>Remove <var>NODE</var> from <var>POOL</var></li>
</ol></li>
</ol></li>
<li>If no <a title="node">nodes</a> are distributed to <var>CONTENT</var>:
<ol>
<li>For each child, <var>CHILD</var>, of <var>CONTENT</var>
<ol>
<li><a title="distributes">Distribute</a> <var>CHILD</var> into <var>CONTENT</var></li>
</ol></li>
</ol></li>
</ol></li>
</ol>
</div>
<p class="note">If no nodes are distributed into a <a>content insertion point</a> <var>CONTENT</var>, the child <a title="node">nodes</a> of <var>CONTENT</var> are distributed into <var>CONTENT</var> as fallback nodes.</p>
<p>If any condition which affects the <a>distribution result</a> changes, the <a>distribution result</a> <strong>must</strong> be updated before any use of the <a>distribution result</a>.</p>
</section>
<section>
<h3>Satisfying Matching Criteria</h3>
<p>The <dfn>matching criteria</dfn> for an <a>insertion point</a> is a set of <a title="compound selector">compound selectors</a> [[!SELECTORS4]]. These <a title="compound selector">compound selectors</a> are restricted to contain only these <a title="simple selector">simple selectors</a>:</p>
<ul>
<li>A <a>type selector</a> or a <a>universal selector</a></li>
<li><a title="class selector">class selector(s)</a></li>
<li>An <a>ID selector</a></li>
<li><a title="attribute selector">attribute selector(s)</a></li>
<li>A <a>negation pseudo-class</a>, <code>:not()</code></li>
</ul>
<p>A <a>node</a> <dfn title="satisfies-matching-criteria">satisfies</dfn> a <a>matching criteria</a> only if:</p>
<ol>
<li>all <a title="compound selector">compound selectors</a> in the set, contain only the <a title="simple selector">simple selectors</a> specified above; and</li>
<li>a <a>node</a> matches at least one <a title="compound selector">compound selectors</a> in the set or the set is empty.</li>
</ol>
</section>
</section>
<section>
<h2>Composition</h2>
<p>The <dfn>composed tree children calculation algorithm</dfn> <strong>must</strong> be used to determine the child <a title="node">nodes</a> of a <a>node</a> in the <a>composed tree</a> and <strong>must</strong> be <a title="processing equivalence">equivalent</a> to processing the following steps:</p>
<div class="algorithm">
<dl>
<dt>Input</dt>
<dd><var>NODE</var>, a <a>node</a> which participates in a composed tree</dd>
<dt>Output</dt>
<dd><var>CHILDREN</var>, the child nodes of <var>NODE</var> in the <a>composed tree</a>.</dd>
</dl>
<ol>
<li>Let <var>CHILDREN</var> be an empty ordered list of nodes</li>
<li>If <var>NODE</var> is a <a>shadow host</a>:
<ol>
<li>Let <var>CHILD-POOL</var> be the children of the <a>youngest shadow root</a> which <var>NODE</var> <a>hosts</a>.</li>
</ol></li>
<li>Otherwise:
<ol>
<li>Let <var>CHILD-POOL</var> be the child <a title="node">nodes</a> of NODE</li>
</ol></li>
<li>For each <a>node</a>, <var>CHILD</var>, in <var>CHILD-POOL</var>:
<ol>
<li>If <var>CHILD</var> is an <a>insertion point</a>:
<ol>
<li>For each <a>node</a>, <var>DISTRIBUTED-NODE</var>, in the <a>distributed nodes</a> of the <a>insertion point</a> <var>CHILD</var>:
<ol>
<li>If <var>CHILD</var> is the <a>final destination</a> of <var>DISTRIBUTED-NODE</var>, add <var>DISTRIBUTED-NODE</var> to <var>CHILDREN</var></li>
</ol></li>
</ol></li>
<li>Otherwise:
<ol>
<li>Add <var>CHILD</var> to <var>CHILDREN</var></li>
</ol></li>
</ol></li>
</ol>
</div>
<p>For a given <a>tree of trees</a> <var>TREE-OF-TREES</var>, the <a>composed tree</a> constructed from <var>TREE-OF-TREES</var> <strong>must</strong> be <a title="processing equivalence">equivalent</a> to the following tree:</p>
<ul>
<li>The <a>root</a> <a>node</a> of the <a>composed tree</a> is the <a>root</a> <a>node</a> of the <a>root tree</a> of <var>TREE-OF-TREES</var>.</li>
<li>For a given <a>node</a> which <a>participates</a> in the <a>composed tree</a>, the child <a title="node">nodes</a> of the <a>node</a> is the result of the <a>composed tree children calculation algorithm</a> with the <a>node</a> as input.
</li>
</ul>
</section>
<section>
<h2>Events</h2>
<p>In each algorithm in this section, the <a>Window</a> <strong>must</strong> be considered as if it were the parent node of the <a>Document</a> so that the <a>Window</a> also receives an <a>event</a>.</p>
<p>When an <a>event</a> is <a title="event dispatch">dispatched</a> in a <a>shadow tree</a>, its path either crosses the <a title="shadow tree">shadow trees</a> or is terminated at the <a>shadow root</a>. One exception are the <a title="mutation event">mutation events</a>. The <a title="mutation event">mutation event types</a> <strong>must</strong> never be dispatched in a <a>shadow tree</a>.</p>
<section>
<h3>Events that are Always Stopped</h3>
<p>The <dfn title="events-always-stopped">following events</dfn> <strong>must</strong> always be stopped at the <a>root</a> <a>node</a> of the <a>node tree</a>:</p>
<ul>
<li><code>abort</code></li>
<li><code>error</code></li>
<li><code>select</code></li>
<li><code>change</code></li>
<li><code>load</code></li>
<li><code>reset</code></li>
<li><code>resize</code></li>
<li><code>scroll</code></li>
<li><code>selectstart</code></li>
</ul>
</section>
<section>
<h3>Event Paths</h3>
<p>The <dfn>event path calculation algorithm</dfn> must be used to determine event path and <strong>must</strong> be <a title="processing equivalence">equivalent</a> to processing the following steps:</p>
<div class="algorithm">
<dl>
<dt>Input</dt>
<dd><var>NODE</var>, a node</dd>
<dd><var>EVENT</var>, an event</dd>
<dt>Output</dt>
<dd><var>PATH</var>, an event path, a ordered list of an event target</dd>
</dl>
<ol>
<li>Let <var>PATH</var> be the empty ordered list of nodes</li>
<li>Let <var>CURRENT</var> be <var>NODE</var></li>
<li>Add <var>CURRENT</var> to <var>PATH</var></li>
<li>Repeat while <var>CURRENT</var> exists:
<ol>
<li>If the <a>destination insertion points</a> of <var>CURRENT</var> is not empty:
<ol>
<li>For each <a>insertion point</a>, <var>INSERTION-POINT</var>, in the <a>destination insertion points</a> of <var>CURRENT</var>:
<ol>
<li>If <var>INSERTION-POINT</var> is a <a>shadow insertion point</a>:
<ol>
<li>Let <var>SHADOW-ROOT</var> be the <a>root</a> <a>node</a> of <var>INSERTION-POINT</var></li>
<li>If <var>SHADOW-ROOT</var> is not the <a>oldest shadow root</a>:
<ol>
<li>Add the <a>older shadow root</a> relative to <var>SHADOW-ROOT</var> to <var>PATH</var></li>
</ol></li>
</ol></li>
<li>Add <var>INSERTION-POINT</var> to <var>PATH</var></li>
</ol></li>
<li>Let <var>CURRENT</var> be the <a>final destination</a> of <var>CURRENT</var></li>
</ol></li>
<li>Otherwise:
<ol>
<li>If <var>CURRENT</var> is a <a>shadow root</a>:
<ol>
<li>Let <var>SHADOW-HOST</var> be the <a>shadow host</a> which <a>hosts</a> <var>CURRENT</var></li>
<li>If <var>SHADOW-HOST</var> <a>hosts</a> the <a>node tree</a> which <var>NODE</var> <a>participates</a> in and <var>EVENT</var> is one of the <a title="events-always-stopped">events which must be stopped</a>:
<ol>
<li>Stop this algorithm</li>
</ol></li>
<li>Let <var>CURRENT</var> be the <a>shadow host</a> which <a>hosts</a> <var>CURRENT</var></li>
<li>Add <var>CURRENT</var> to <var>PATH</var></li>
</ol></li>
<li>Otherwise:
<ol>
<li>Let <var>CURRENT</var> be the <a>parent</a> <a>node</a> of <var>CURRENT</var></li>
<li>If <var>CURRENT</var> exists:
<ol>
<li>Add <var>CURRENT</var> to <var>PATH</var></li>
</ol></li>
</ol></li>
</ol></li>
</ol></li>
</ol>
</div>
</section>
<section class="informative">
<h3>Event Paths Example</h3>
<p>
Suppose we have the following tree of trees:
</p>
<figure>
<object data="../../assets/images/event-path-tree-of-trees.svg" width="301" height="1074"></object>
<figcaption>An example tree of trees. Nodes which are not involved in the example event path, which is explained later, are omitted.</figcaption>
</figure>
<ul>
<li>
<code>A</code> is a <a>document</a>.
</li>
<li>
<code>E</code>, <code>J</code>, <code>N</code>, <code>Q</code>, <code>S</code> and <code>V</code> are <a title="shadow root">shadow roots</a>.
</li>
<li>
<code>I</code>, <code>M</code>, <code>P</code>, <code>R</code> and <code>U</code> are <a title="content insertion point">content insertion points</a>.
</li>
<li>
<code>X</code> is a <a>shadow insertion point</a>.
</li>
</ul>
<p>
This <a>tree of trees</a> has the following seven <a title="node tree">node trees</a>, one <a>document tree</a> and six <a title="shadow tree">shadow trees</a>:
</p>
<ul>
<li>
The <var>document tree 1</var>. Node <code>A</code>, <code>B</code>, <code>C</code> and <code>D</code> participate in that.
</li>
<li>
The <var>shadow tree 2</var> hosted by <code>B</code>. Node <code>E</code>, <code>F</code>, <code>G</code>, <code>H</code> and <code>I</code> participate in that.
</li>
<li>
The <var>shadow tree 3</var> hosted by <code>H</code>. Node <code>J</code>, <code>K</code>, <code>L</code> and <code>M</code> participate in that.
</li>
<li>
The <var>shadow tree 4</var> hosted by <code>K</code>. Node <code>N</code>, <code>O</code> and <code>P</code> participate in that.
</li>
<li>
The <var>shadow tree 5</var> hosted by <code>O</code>. Node <code>Q</code> and <code>R</code> participate in that.
</li>
<li>
The <var>shadow tree 6</var> hosted by <code>F</code>. Node <code>S</code>, <code>T</code> and <code>U</code> participate in that.
</li>
<li>
The <var>shadow tree 7</var> hosted by <code>B</code>. Node <code>V</code>, <code>W</code> and <code>X</code> participate in that.
This <a>shadow tree</a> is younger than the <var>shadow tree 2</var>.
</li>
</ul>
<p>
Let's assume that the <a>distribution result</a> of this <a>tree of trees</a> is:
</p>
<ul>
<li>
The <a>destination insertion points</a> of <code>C</code> are <code>[I, M]</code> (<code>C</code> is re-distributed)
</li>
<li>
The <a>destination insertion points</a> of <code>L</code> are <code>[P, R]</code> (<code>L</code> is re-distributed)
</li>
<li>
The <a>destination insertion points</a> of <code>G</code> are <code>[U]</code>
</li>
<li>
The <a>destination insertion points</a> of <code>F</code> are <code>[X]</code>
</li>
</ul>
<p>
In this case, if an event is dispatched on node <code>D</code>, the event path will be:
</p>
<p>
<code>
[D, C, I, M, L, P, R, Q, O, N, K, J, H, G, U, T, S, F, E, X, W, V, B, A] (<a>Window</a> is omitted)
</code>
</p>
<p>
Note that the <a>event path calculation algorithm</a> is designed to achieve the following goals:
</p>
<ol>
<li>
If there is a node, <var>CHILD</var>, in the event path and <var>CHILD</var> has a parent node, <var>PARENT</var>, in the node tree, the event path also includes <var>PARENT</var>.
<var>PARENT</var> always appears somewhere after <var>CHILD</var> in the event path.
</li>
<li>
Nodes in the event path form a <em>linear ancestor chain</em> in each <a>node tree</a>. There are no <em>branch points</em> in each <a>node tree</a>.
</li>
</ol>
<figure>
<object data="../../assets/images/event-path-node-trees.svg" width="884" height="473">></object>
<figcaption>
The relationship between an event path and node trees. In the figure, a number shown in a left-side of each node represents a zero-based position of each node in the event path.
A parent node always have a larger number than that of its child node in each node tree.
</figcaption>
</figure>
<p>
That means if we focus on one <a>node tree</a> and forget all other <a title="node tree">node trees</a>,
the event path would be seen as if the event happened only on the <a>node tree</a> which we are focused on.
This is an important aspect in a sense that hosting shadow trees doesn't have any effect to the event path <em>within</em> the <a>node tree</a> the <a>shadow host</a> participate in
as long as the event is not stopped somewhere in the <a title="descendant tree">descendant trees</a>.
</p>
<p>
For example, from the view of the <var>document tree 1</var>, the event path would be seen as <code>[D, C, B, A]</code>.
From the view of the <var>shadow tree 2</var>, the event path would be seen as <code>[I, H, G, F, E]</code>.
The similar things also apply to other <a title="node tree">node trees</a>.
</p>
<p>
It is also worth pointing out that if we exclude all <a title="insertion point">insertion points</a> and <a title="shadow root">shadow roots</a> from an event path,
the result would be equivalent to the inclusive ancestors of the node on which the event is dispatched, in the composed tree.
</p>
<figure>
<object data="../../assets/images/event-path-and-composed-tree.svg" width="217" height="1723"></object>
<figcaption>
The relationship between an event path and the <a>composed tree</a>. The event path used in the example is shown in the left-hand side and the <a>composed tree</a> is shown in the right-hand side.
If we exclude all <a title="insertion point">insertion points</a> and <a title="shadow root">shadow roots</a> from the event path,
the result would be equivalent to the inclusive ancestors of the node, <code>D</code>, in the <a>composed tree</a>.
</figcaption>
</figure>
</section>
<section>
<h3>Event Retargeting</h3>
<p>In the cases where event path is across multiple node trees, the event's information about the target of the event is adjusted in order to maintain <a href="#encapsulation">encapsulation</a>. Event <dfn>retargeting</dfn> is a process of computing relative targets for each ancestor of the <a>node</a> at which the event is dispatched. A <dfn>relative target</dfn> is a <a>node</a> that most accurately represents the target of a dispatched event at a given ancestor while maintaining the encapsulation.</p>
<p>The <dfn>retargeting algorithm</dfn> is used to determine relative targets, and it <strong>must</strong> be <a title="processing equivalence">equivalent</a> to processing the following steps:</p>
<div class="algorithm">
<dl>
<dt>Input</dt>
<dd><var>EVENT-PATH</var>, an event path</dd>
<dd><var>CURRENT-TARGET</var>, a <a>node</a> where the event listener is invoked.</dd>
<dt>Output</dt>
<dd><var>RELATIVE-TARGET</var>, adjusted target</dd>
</dl>
<ol>
<li>Let <var>CURRENT-TARGET-TREE</var> be the <a>node tree</a> which <var>CURRENT-TARGET</var> <a>participates</a> in</li>
<li>Let <var>ORIGINAL-TARGET</var> be the first item in <var>EVENT-PATH</var></li>
<li>Let <var>ORIGINAL-TARGET-TREE</var> be the <a>node tree</a> which <var>ORIGINAL-TARGET</var> <a>participates</a> in</li>
<li>Let <var>RELATIVE-TARGET-TREE</var> be the lowest common <a>inclusive ancestor tree</a> of <var>CURRENT-TARGET-TREE</var> and <var>ORIGINAL-TARGET-TREE</var></li>
<li>Let <var>RELATIVE-TARGET</var> be the first <a>node</a> in <var>EVENT-PATH</var> which satisfies the following condition:
<ol>
<li>The <a>node</a> <a>participates</a> in <var>RELATIVE-TARGET-TREE</var></li>
</ol>
</li>
</ol>
</div>
<p>The retargeting process <strong>must</strong> occur prior to dispatch of an event.</p>
</section>
<section>
<h3>Retargeting <code>relatedTarget</code></h3>
<p>Some events have a <a><code>relatedTarget</code></a> [[!DOM-Level-3-Events]] property, which holds a <a>node</a> that's not the event's target, but is related to the event.</p>
<p>For instance, a <code>mouseover</code> event's <a><code>relatedTarget</code></a> may hold the <a>node</a> from which the mouse has moved to event's <code>target</code>. In the case where <code>relatedTarget</code> is in a <a>shadow tree</a>, the conforming UAs <strong>must</strong> not leak its actual value outside of this tree. In cases where both <code>relatedTarget</code> and <code>target</code> are part of the same <a>shadow tree</a>, the conforming UAs <strong>must</strong> <em>stop</em> events at the shadow root to avoid the appearance of spurious <code>mouseover</code> and <code>mouseout</code> events firing from the same node.</p>
<p>Thus, if an event has a <code>relatedTarget</code>, its value and extent of event dispatch <strong>must</strong> be adjusted. In general:</p>
<ol>
<li>For a given node, the <code>relatedTarget</code> <strong>must</strong> be changed to its ancestor (or self) that is in the same <a>shadow tree</a> as the node</li>
<li>Event listeners <strong>must not</strong> be invoked on a <a>node</a> for which the <code>target</code> and <code>relatedTarget</code> are the same.</li>
</ol>
<p>The <dfn>related target resolution algorithm</dfn> <strong>must</strong> be used to determine the value of the <a><code>relatedTarget</code></a> property and <strong>must</strong> be <a title="processing equivalence">equivalent</a> to processing the following steps:</p>
<div class="algorithm">
<dl>
<dt>Input</dt>
<dd><var>EVENT</var>, an event</dd>
<dd><var>CURRENT-TARGET</var>, the <a>node</a> on which event listeners would be invoked</dd>
<dd><var>RELATED-TARGET</var>, the related target for the event</dd>
<dt>Output</dt>
<dd><var>ADJUSTED-RELATED-TARGET</var>, the <dfn>adjusted related target</dfn> for <var>CURRENT-TARGET</var></dd>
</dl>
<ol>
<li>Let <var>CURRENT-TARGET-TREE</var> be the <a>node tree</a> which <var>CURRENT-TARGET</var> <a>participates</a> in</li>
<li>Let <var>RELATED-TARGET-TREE</var> be the <a>node tree</a> which <var>RELATED-TARGET</var> <a>participates</a> in</li>
<li>Let <var>RELATED-TARGET-EVENT-PATH</var> be the result of the <a>event path calculation algorithm</a> with <var>RELATED-TARGET</var> and <var>EVENT</var> as input</li>
<li>If <var>CURRENT-TARGET-TREE</var> and <var>RELATED-TARGET-TREE</var> participate in the same <a>tree of trees</a>:
<ol>
<li>Let <var>LOWEST-COMMON-ANCESTOR-TREE</var> be the lowest common <a>inclusive ancestor tree</a> of <var>CURRENT-TARGET-TREE</var> and <var>RELATED-TARGET-TREE</var></li>
</ol>
</li>
<li>Otherwise:
<ol>
<li>Let <var>LOWEST-COMMON-ANCESTOR-TREE</var> be the <a>root tree</a> of <var>RELATED-TARGET-TREE</var></li>
</ol>
</li>
<li>For each <a>inclusive ancestor tree</a>, <var>COMMON-ANCESTOR-TREE</var>, of the <var>LOWEST-COMMON-ANCESTOR-TREE</var>, in ascending order:
<ol>
<li>Let <var>ADJUSTED-RELATED-TARGET</var> be the first <a>node</a> in <var>RELATED-TARGET-EVENT-PATH</var> which satisfies the following condition:
<ol>
<li>The <a>node</a> <a>participates</a> in <var>COMMON-ANCESTOR-TREE</var></li>
</ol>
</li>
<li>If such a <var>ADJUSTED-RELATED-TARGET</var> exists:
<ol>
<li>Stops this algorithm</li>
</ol>
</li>
</ol>
</li>
</ol>
</div>
<p class="note">The result of the related target resolution algorithm is not always null. Unless that, you should file a bug for this specification.</p>
<p>The relatedTarget retargeting process <strong>must</strong> occur prior to dispatch of an event.</p>
</section>
<section>
<h3>Retargeting Touch Events</h3>
<p>The <a><code>Touch</code></a> <a title="Touch target"><code>target</code></a> [[!TOUCH-EVENTS]] attribute must be adjusted in the same way as an event with a <a><code>relatedTarget</code></a>. Each <a><code>Touch</code></a> <a title="Touch target"><code>target</code></a> in the <a><code>TouchList</code></a> returned from <a><code>TouchEvent</code></a> <a title="touches"><code>touches()</code></a>, <a title="changedTouches"><code>changedTouches()</code></a> and <a title="targetTouches"><code>targetTouches()</code></a> must be the result of <a>related target resolution algorithm</a>, given <var>NODE</var> and <a><code>Touch</code></a> <a title="Touch target"><code>target</code></a> as arguments.</p>
</section>
<section>
<h3>Retargeting Focus Events</h3>
<p>The <code>focus</code>, <code>DOMFocusIn</code>, <code>blur</code>, and <code>DOMFocusOut</code> events <strong>must</strong> be treated in the same way as events with a <code>relatedTarget</code>, where the corresponding <a>node</a> that is losing focus as a result of <code>target</code> gaining focus or the <a>node</a> that is gaining focus, and thus causing the blurring of <code>target</code> acts as the related target.</p>
</section>
<section>
<h3>Event Dispatch</h3>
<p>At the time of event dispatch:</p>
<ul>
<li>The <a><code>Event</code></a> <a><code>target</code></a> and <a><code>currentTarget</code></a> attributes <strong>must</strong> return the <a>relative target</a> for the <a>node</a> on which event listeners are <a title="event listener invoke">invoked</a></li>
<li>The <a><code>MouseEvent</code></a> <a><code>relatedTarget</code></a> attribute <strong>must</strong> return the <a>adjusted related target</a></li>
<li>The <a><code>MouseEvent</code></a> <a><code>offsetX</code></a> and <a><code>offsetY</code></a> attributes <strong>must</strong> return the coordinates relative to the origin of the <a>padding edge</a> of the <a>relative target</a></li>
<li>The <a><code>Touch</code></a> <a title="Touch target"><code>target</code></a> attribute <strong>must</strong> return the <a>adjusted related target</a></li>
<li>If the <a><code>relatedTarget</code></a> and <a><code>target</code></a> are the same for a given node, its the event listeners <strong>must not</strong> be invoked. <a><code>TouchEvent</code></a> is not subject to this rule.</li>
<li>When <em>capturing</em>, which entails processing step 6 of the <a title="event dispatch">event dispatch algorithm</a>, the event listeners <strong>must not</strong> be <a title="event listener invoke">invoked</a> on a <a>node</a> <strong>if</strong> it is the same as its <a>relative target</a></li>
<li>When <em>bubbling</em>, which entails processing step 9 of the <a title="event dispatch">event dispatch algorithm</a>, the <a><code>Event</code></a> <a>eventPhase</a> attribute <strong>must</strong> return <a>AT_TARGET</a> <strong>if</strong> the <a>relative target</a> is same as the <a>node</a> on which event listeners are <a title="event listener invoke">invoked</a></li>
<li>If the event's <a><code>bubbles</code></a> attribute value is <strong>false</strong>, run these substeps:
<ol>
<li>Reverse the order of <em>event path</em></li>
<li>Initialize event's <a><code>eventPhase</code></a> attribute to <a><code>AT_TARGET</code></a></li>
<li>For each object in <em>event path</em> where the <a>relative target</a> is same as the object, <a title="event listener invoke">invoke</a> its <a title="event listener">event listeners</a>, with event <em>event</em>, as long as <em>event</em>'s <a>stop propagation flag</a> is unset</li>
</ol></li>
</ul>
<p>Upon completion of the event dispatch, the <a><code>Event</code></a> object's <a><code>target</code></a> and <a><code>currentTarget</code></a> <strong>must</strong> be to the highest ancestor's <a>relative target</a>. Since it is possible for a script to hold on to the <code>Event</code> object past the scope of event dispatch, this step is necessary to avoid revealing the <a title="node">nodes</a> in <a title="shadow tree">shadow trees</a>.</p>
</section>
<section class="informative">
<h3>Event Retargeting Example</h3>
<p>Suppose we have a user interface for a media controller, represented by this tree, composed of both <a>document tree</a> and the <a title="shadow tree">shadow trees</a>. In this example, we will assume that selectors are allowed to cross the shadow boundaries and we will use these selectors to identify the <a title="element">elements</a>. Also, we will invent a fictional <code>shadow-root</code> <a>element</a> to demarcate the shadow boundaries and represent <a title="shadow root">shadow roots</a>:</p>
<pre class="example">
<div id="player">
<span class=shadow-boundary><shadow-root id="player-shadow-root"></span>
<div id="controls">
<button id="play-button">PLAY</button>
<input type="range" id="timeline">
<span class=shadow-boundary><shadow-root id="timeline-shadow-root"></span>
<div id="slider-thumb" id="timeline-slider-thumb"></div>
<span class=shadow-boundary></shadow-root></span>
</input>
<div id="volume-slider-container">
<input type="range" id="volume-slider">
<span class=shadow-boundary><shadow-root id="volume-shadow-root"></span>
<div id="slider-thumb" id="volume-slider-thumb"></div>
<span class=shadow-boundary></shadow-root></span>
</input>
</div>
</div>
<span class=shadow-boundary></shadow-root></span>
</div>
</pre>
<p>Let's have a user position their pointing device over the volume slider's thumb (<code>#volume-slider-thumb</code>), thus triggering a <code>mouseover</code> event on that node. For this event, let's pretend it has no associated <code>relatedTarget</code>.</p>
<p>Per the <a>retargeting algorithm</a>, we should have the following set of ancestors and relative targets:</p>
<table>
<thead>
<tr>
<th>Ancestor</th>
<th>Relative Target</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>#player</code></td>
<td><code><strong>#player</strong></code></td>
</tr>
<tr>
<td><code>#player-shadow-root</code></td>
<td><code>#volume-slider</code></td>
</tr>
<tr>
<td><code>#controls</code></td>
<td><code>#volume-slider</code></td>
</tr>
<tr>
<td><code>#volume-slider-container</code></td>
<td><code>#volume-slider</code></td>
</tr>
<tr>
<td><code>#volume-slider</code></td>
<td><code><strong>#volume-slider</strong></code></td>
</tr>
<tr>
<td><code>#volume-shadow-root</code></td>
<td><code>#volume-slider-thumb</code></td>
</tr>
<tr>
<td><code>#volume-slider-thumb</code></td>
<td><code><strong>#volume-slider-thumb</strong></code></td>
</tr>
</tbody>
</table>
<p>After we dispatch the <code>mouseover</code> event using these newly computed relative targets, the user decides to move their pointing device over the thumb of the timeline
(<code>#timeline-slider-thumb</code>). This triggers both a <code>mouseout</code> event for the volume slider thumb and the <code>mouseover</code> event for the timeline thumb.</p>
<p>Let's see how the <code>relatedTarget</code> value of the volume thumb's <code>mouseout</code> event is affected. For this event, the <code>relatedTarget</code> is the timeline thumb (<code>#timeline-slider-thumb</code>). Per the <a>related target resolution algorithm</a>, we should have the following set of ancestors and adjusted related targets:</p>
<table>
<thead>
<tr>
<th>Ancestor</th>
<th>Relative Target</th>
<th>Adjusted related Target</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>#player</code></td>
<td><code><strong>#player</strong></code></td>
<td><code><strong>#player</strong></code></td>
</tr>
<tr>
<td><code>#player-shadow-root</code></td>
<td><code>#volume-slider</code></td>
<td><code>#timeline</code></td>
</tr>
<tr>
<td><code>#controls</code></td>
<td><code>#volume-slider</code></td>
<td><code>#timeline</code></td>
</tr>
<tr>
<td><code>#volume-slider-container</code></td>
<td><code>#volume-slider</code></td>
<td><code>#timeline</code></td>
</tr>
<tr>
<td><code>#volume-slider</code></td>
<td><code><strong>#volume-slider</strong></code></td>
<td><code>#timeline</code></td>
</tr>
<tr>
<td><code>#volume-shadow-root</code></td>
<td><code>#volume-slider-thumb</code></td>
<td><code>#timeline</code></td>
</tr>
<tr>
<td><code>#volume-slider-thumb</code></td>
<td><code><strong>#volume-slider-thumb</strong></code></td>
<td><code><strong>#timeline</strong></code></td>
</tr>
</tbody>
</table>
<p>The node, <code>#player</code>, has both <code>target</code> and <code>relatedTarget</code> being the same value (<code>#player</code>), which means that we do not dispatch the event on this <a>node</a> and its ancestors.</p>
</section>
</section>
<section>
<h2>User Interaction</h2>
<section class="informative">
<h3>Ranges and Selections</h3>
<p>
<a>Selection</a> [[!EDITING]] is not defined. Implementation should do their best to do what's best for them. Here's one possible, admittedly naive way:
</p>
<p>Since <a title="node">nodes</a> which are in the different <a title="node tree">node trees</a> never have the same <a>root</a>, there may never exist a valid <a title="range">DOM range</a> that spans multiple <a title="node tree">node trees</a>.</p>
<p>Accordingly, <a title="selection">selections</a> may only exist within one <a>node tree</a>, because they are defined by a single <a>range</a>. The <a>selection</a>, returned by the <a><code>window.getSelection()</code></a> method never returns a <a>selection</a> within a <a>shadow tree</a>.</p>
<p>The <code>getSelection()</code> method of the <a>shadow root</a> object returns the current <a>selection</a> in this <a>shadow tree</a>.</p>
</section>
<section>
<h3>Focus Navigation</h3>