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Introduce browsing context groups
The grouping concepts unit of related browsing contexts and unit of similar-origin browsing contexts were not accurate, due to browsing contexts being able to hold a sequence of (potentially cross-site) documents. Fixes whatwg#4198.
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@@ -2637,6 +2637,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
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<ul class="brief">
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<li><dfn data-x="concept-host" data-x-href="https://url.spec.whatwg.org/#concept-host">host</dfn></li>
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<li><dfn data-x-href="https://url.spec.whatwg.org/#host-public-suffix">public suffix</dfn></li>
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<li><dfn data-x-href="https://url.spec.whatwg.org/#host-same-site">same site</dfn></li>
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<li><dfn data-x="concept-domain" data-x-href="https://url.spec.whatwg.org/#concept-domain">domain</dfn></li>
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<li><dfn data-x-href="https://url.spec.whatwg.org/#concept-ipv4">IPv4 address</dfn></li>
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<li><dfn data-x-href="https://url.spec.whatwg.org/#concept-ipv6">IPv6 address</dfn></li>
@@ -77202,7 +77203,10 @@ dictionary <dfn>DragEventInit</dfn> : <span>MouseEventInit</span> {
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context</dfn>:</p>
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<ol>
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<li><p>Return the result of <span>creating a new browsing context</span> with null.</p></li>
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<li><p>Let <var>group</var> be the result of <span>creating a new browsing context
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group</span>.</p></li>
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<li><p>Return <var>group</var>'s <span>browsing context set</span>[0].</p></li>
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</ol>
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<p class="note">This creates a <span>top-level browsing context</span>.</p>
@@ -77214,6 +77218,13 @@ dictionary <dfn>DragEventInit</dfn> : <span>MouseEventInit</span> {
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<li><p>Let <var>browsingContext</var> be the result of <span>creating a new browsing
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context</span> with <var>opener</var>'s <span>active document</span>.</p></li>
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<li><p>Assert: <var>opener</var>'s <span>top-level browsing context</span>'s <span data-x="tlbc
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group">group</span> is non-null, as <span data-x="navigate">navigating</span> invokes this
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directly.</p></li>
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<li><p><span data-x="bcg append">Append</span> <var>browsingContext</var> to <var>opener</var>'s
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<span>top-level browsing context</span>'s <span data-x="tlbc group">group</span>.</p></li>
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<li><p>Set <var>browsingContext</var>'s <span>opener browsing context</span> to
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<var>opener</var>.</p></li>
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@@ -77303,6 +77314,9 @@ dictionary <dfn>DragEventInit</dfn> : <span>MouseEventInit</span> {
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data-export="">top-level browsing context</dfn> for itself and all of the browsing contexts for
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which it is an <span>ancestor browsing context</span>.</p>
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<p>A <span>top-level browsing context</span> has an associated <dfn data-x="tlbc
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group">group</dfn> (null or a <span>browsing context group</span>). It is initially null.</p>
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<p>It is possible to create new browsing contexts that are related to a <span>top-level browsing
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context</span> without being nested through an element. Such browsing contexts are called <dfn
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data-x="auxiliary browsing context" data-lt="auxiliary browsing context" data-export="">auxiliary
@@ -77694,36 +77708,72 @@ console.assert(iframeWindow.frameElement === null);
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<h4>Groupings of browsing contexts</h4>
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<p>Each <span>browsing context</span> is defined as having a list of one or more <dfn>directly
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reachable browsing contexts</dfn>. These are:</p>
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<p>A user agent holds a <dfn>browsing context group set</dfn> (a <span>set</span> of <span
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data-x="browsing context group">browsing context groups</span>).</p>
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<ul>
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<p>A <dfn>browsing context group</dfn> holds a <dfn>browsing context set</dfn> (a <span>set</span>
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of <span data-x="top-level browsing context">top-level browsing contexts</span>).</p>
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<p>To <dfn data-x="creating a new browsing context group">create a new browsing context
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group</dfn>, run these steps:</p>
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<li>The <span>browsing context</span> itself.</li>
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<ol>
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<li><p>Let <var>group</var> be a new <span>browsing context group</span>.</p></li>
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<li><p><span data-x="set append">Append</span> <var>group</var> to the user agent's
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<span>browsing context group set</span>.</p></li>
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<li>All the <span>browsing context</span>'s <span data-x="child browsing context">child browsing
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contexts</span>.</li>
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<li><p><span data-x="bcg append">Append</span> the result of <span>creating a new browsing
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context</span> with null to <var>group</var>.</p></li>
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<li>The <span>browsing context</span>'s <span>parent browsing context</span>.</li>
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<li><p>Return <var>group</var>.</p></li>
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</ol>
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<li>All the <span data-x="browsing context">browsing contexts</span> that have the <span>browsing
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context</span> as their <span>opener browsing context</span>.</li>
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<p>To <dfn data-x="bcg append">append</dfn> a <span>top-level browsing context</span>
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<var>browsingContext</var> to a <span>browsing context group</span> <var>group</var>, run these
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steps:</p>
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<li>The <span>browsing context</span>'s <span>opener browsing context</span>.</li>
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<ol>
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<li><p><span data-x="set append">Append</span> <var>browsingContext</var> to <var>group</var>'s
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<span>browsing context set</span>.</p></li>
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</ul>
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<li><p>Set <var>browsingContext</var>'s <span data-x="tlbc group">group</span> to
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<var>group</var>.</p></li>
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</ol>
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<p>To <dfn data-x="bcg remove">remove</dfn> a <span>top-level browsing context</span>
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<var>browsingContext</var>, run these steps:</p>
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<ol>
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<li><p>Assert: <var>browsingContext</var>'s <span data-x="tlbc group">group</span> is non-null,
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because a <span>browsing context</span> only gets <span data-x="a browsing context is
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discarded">discarded</span> once.</p></li>
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<li><p>Let <var>group</var> be <var>browsingContext</var>'s <span data-x="tlbc
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group">group</span>.</p></li>
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<li><p>Set <var>browsingContext</var>'s <span data-x="tlbc group">group</span> to null.</p></li>
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<p>The transitive closure of all the <span data-x="browsing context">browsing contexts</span> that
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are <span>directly reachable browsing contexts</span> forms a <dfn>unit of related browsing
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contexts</dfn>.</p>
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<li><p><span data-x="list remove">Remove</span> <var>browsingContext</var> from
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<var>group</var>'s <span>browsing context set</span>.</p></li>
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<p>Each <span>unit of related browsing contexts</span> is then further divided into the smallest
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number of groups such that every member of each group has an <span>active document</span> with an
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<span>origin</span> that, through appropriate manipulation of the <code
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data-x="dom-document-domain">document.domain</code> attribute, could be made to be <span>same
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origin-domain</span> with other members of the group, but could not be made the same as members of
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any other group. Each such group is a <dfn data-export="">unit of related similar-origin browsing
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contexts</dfn>.</p>
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<li><p>If <var>group</var>'s <span>browsing context set</span> <span data-x="list is empty">is
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empty</span>, then <span data-x="list remove">remove</span> <var>group</var> from the user
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agent's <span>browsing context group set</span>.</p></li>
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</ol>
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<p class="note"><span data-x="bcg append">Append</span> and <span data-x="bcg
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remove">remove</span> are primitive operations that help define the lifetime of a <span>browsing
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context group</span>. They are called from <span>creating a new browsing context group</span>,
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<span>creating a new auxiliary browsing context</span>, and <span data-x="a browsing context is
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discarded">discarding a browsing context</span>.</p>
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<hr>
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<p class="note">The HTML Standard used to define "<span
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id="unit-of-related-browsing-contexts">unit of related browsing contexts</span>" and "<span
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id="unit-of-related-similar-origin-browsing-contexts">unit of related similar-origin browsing
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contexts</span>". These have been removed as they were not adequate.</p>
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</div>
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@@ -77919,7 +77969,7 @@ console.assert(iframeWindow.frameElement === null);
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most recently focused, or more closely related.</p>
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<p class="&#x0058;&#x0058;&#x0058;">This will be made more precise in <a
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href="https://github.com/whatwg/html/issues/1440">issue #1440</a>.</p>
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href="https://github.com/whatwg/html/issues/313">issue #313</a>.</p>
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</li>
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<li>
@@ -79007,9 +79057,7 @@ dictionary <dfn>WindowPostMessageOptions</dfn> : <span>PostMessageOptions</span>
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<h4>Garbage collection and browsing contexts</h4>
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<p>A <span>browsing context</span> has a strong reference to each of its <code>Document</code>
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objects (due to its <span>session history</span>) and its <code>WindowProxy</code> object, and the
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user agent itself has a strong reference to its <span data-x="top-level browsing
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context">top-level browsing contexts</span>.</p>
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objects (due to its <span>session history</span>) and its <code>WindowProxy</code> object.</p>
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<p>A <code>Document</code> has a strong reference to its <code>Window</code> object.</p>
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@@ -79057,14 +79105,20 @@ dictionary <dfn>WindowPostMessageOptions</dfn> : <span>PostMessageOptions</span>
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</ol>
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<p>When <dfn data-export="">a <em>browsing context</em> is discarded</dfn>, the strong reference
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from the user agent itself to the <span>browsing context</span> must be severed, and all the
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<code>Document</code> objects for all the entries in the <span>browsing context</span>'s session
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history must be <span data-x="discard a document">discarded</span> as well.</p>
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<p>To <dfn data-export="" data-x="a browsing context is discarded">discard</dfn> a <span>browsing
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context</span> <var>browsingContext</var>, run these steps:</p>
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<ol>
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<li><p><span data-x="discard a document">Discard</span> all <code>Document</code> objects for all
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the entries in <var>browsingContext</var>'s <span>session history</span>.</p></li>
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<li><p>If <var>browsingContext</var> is a <span>top-level browsing context</span>, then
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<span data-x="bcg remove">remove</span> <var>browsingContext</var>.</p></li>
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</ol>
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<p>User agents may <span data-x="a browsing context is discarded">discard</span> <span
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data-x="top-level browsing context">top-level browsing contexts</span> at any time (typically, in
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response to user requests, e.g. when a user force-closes a window containing one or more <span
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response to user requests, e.g., when a user force-closes a window containing one or more <span
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data-x="top-level browsing context">top-level browsing contexts</span>). Other <span
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data-x="browsing context">browsing contexts</span> must be discarded once their
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<code>WindowProxy</code> object is eligible for garbage collection, in addition to the other
@@ -89045,7 +89099,52 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
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<p class="note">Conceptually, the <span>agent</span> concept is an architecture-independent,
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idealized "thread" in which JavaScript code runs. Such code can involve multiple globals/<span
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data-x="concept-global-object-realm">realms</span> that can synchronously access each other, and
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thus need to run in a single execution thread.</p>
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thus needs to run in a single execution thread.</p>
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<p>To determine whether a <code>Window</code> object <var>A</var> and a <code>Window</code> object
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<var>B</var> are considered <dfn>same-agent <code>Window</code> objects</dfn>, run
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these steps:</p>
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<ol>
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<li>
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<p>If <var>A</var>'s <span>relevant settings object</span>'s <span>responsible browsing
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context</span>'s <span>top-level browsing context</span>'s <span data-x="tlbc
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group">group</span> is not <var>B</var>'s <span>relevant settings object</span>'s
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<span>responsible browsing context</span>'s <span>top-level browsing context</span>'s <span
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data-x="tlbc group">group</span>, then return false.</p>
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<p class="&#x0058;&#x0058;&#x0058;">Unfortunately this model falls apart the moment a
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<span>browsing context</span> is <span data-x="a browsing context is
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discarded">discarded</span>. <a href="https://github.com/whatwg/html/issues/4361">Issue
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#4361</a> sketches a setup that could improve this situation.</p>
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</li>
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<li><p>Let <var>originA</var> be <var>A</var>'s <span>relevant settings object</span>'s <span
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data-x="concept-settings-object-origin">origin</span> and <var>originB</var> be <var>B</var>'s
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<span>relevant settings object</span>'s <span
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data-x="concept-settings-object-origin">origin</span>.</p></li>
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<li><p>If <var>originA</var> is <span>same origin</span> with <var>originB</var>, then return
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true.</p></li>
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<li><p>If <var>originA</var> or <var>originB</var> is not a <span
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data-x="concept-origin-tuple">tuple origin</span>, then return false.</p></li>
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<li><p>If <var>originA</var>'s <span data-x="concept-origin-scheme">scheme</span> is not
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<var>originB</var>'s <span data-x="concept-origin-scheme">scheme</span>, then return
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false.</p></li>
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<li><p>If <var>originA</var>'s <span data-x="concept-origin-host">host</span> is <span>same
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site</span> with <var>originB</var>'s <span data-x="concept-origin-host">host</span>, then return
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true.</p></li>
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<li><p>Return false.</p></li>
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</ol>
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<p class="note">All <span>same-agent <code>Window</code> objects</span> together represent a group
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of <code>Window</code> objects that can synchronously access each other, though sometimes only
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after setting the <code data-x="dom-document-domain">document.domain</code> attribute
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(in)appropriately.</p>
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<p>Until such a time that this standard has a better handle on lifetimes, it defines five types of
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<span data-x="agent">agents</span> that user agents must allocate at the appropriate time.</p>
@@ -89059,14 +89158,12 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
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<dd>
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<p>An <span>agent</span> whose [[CanBlock]] is false and whose set of <span
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data-x="JavaScript realm">realms</span> consists of all <span
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data-x="concept-global-object-realm">realms</span> of <code>Window</code> objects whose
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<span>relevant settings object</span>'s <span>responsible browsing context</span> is in the same
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<span>unit of related similar-origin browsing contexts</span>.</p>
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data-x="concept-global-object-realm">realms</span> of all <span>same-agent <code>Window</code>
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objects</span>.</p>
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<p class="note">Two <code>Window</code> objects that are <span>same origin</span> can be in
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different <span data-x="similar-origin window agent">similar-origin window agents</span>, for
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instance if they are each in their own <span>unit of related similar-origin browsing
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contexts</span>.</p>
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instance if they are each in their own <span>browsing context group</span>.</p>
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</dd>
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<dt><dfn data-export="">Dedicated worker agent</dfn></dt>

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