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Add <template contentmethod> for declarative out-of-order streaming #11818

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Add <template contentmethod> for declarative out-of-order streaming #11818

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6ec5ba3
Add declarative out-of-order streaming
foolip Oct 22, 2025
50a4491
Think out loud with TODOs and questions
foolip Oct 22, 2025
97d3cfd
Flesh things out more
foolip Oct 23, 2025
8739f8b
Let shadowrootmode take precedent over contentmethod
foolip Oct 27, 2025
00872de
Add a note about scope's type
foolip Oct 27, 2025
d99f332
Fix incorrect method descriptions
foolip Oct 29, 2025
5c43560
Define templat's content target element-or-null slot
foolip Nov 6, 2025
cec66b6
Flesh out a lot of details (some in the wrong place/order)
foolip Nov 6, 2025
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176 changes: 170 additions & 6 deletions source
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Original file line number Diff line number Diff line change
Expand Up @@ -13894,6 +13894,7 @@ https://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20HTML%3E%
<li><code data-x="attr-autocorrect">autocorrect</code></li>
<li><code data-x="attr-fe-autofocus">autofocus</code></li>
<li><code data-x="attr-contenteditable">contenteditable</code></li>
<li><code data-x="attr-contentname">contentname</code></li>
<li><code data-x="attr-dir">dir</code></li>
<li><code data-x="attr-draggable">draggable</code></li>
<li><code data-x="attr-enterkeyhint">enterkeyhint</code></li>
Expand Down Expand Up @@ -67863,6 +67864,7 @@ not-slash = %x0000-002E / %x0030-10FFFF
<dd><span data-x="concept-content-nothing">Nothing</span> (for clarification, <a href="#template-example">see example</a>).</dd>
<dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
<dd><span>Global attributes</span></dd>
<dd><code data-x="attr-template-contentmethod">contentmethod</code></dd>
<dd><code data-x="attr-template-shadowrootmode">shadowrootmode</code></dd>
<dd><code data-x="attr-template-shadowrootdelegatesfocus">shadowrootdelegatesfocus</code></dd>
<dd><code data-x="attr-template-shadowrootclonable">shadowrootclonable</code></dd>
Expand All @@ -67879,6 +67881,7 @@ interface <dfn interface>HTMLTemplateElement</dfn> : <span>HTMLElement</span> {
[<span>HTMLConstructor</span>] constructor();

readonly attribute <span>DocumentFragment</span> <span data-x="dom-template-content">content</span>;
[<span>CEReactions</span>] attribute DOMString <span data-x="dom-template-contentmethod">contentMethod</span>;
[<span>CEReactions</span>] attribute DOMString <span data-x="dom-template-shadowrootmode">shadowRootMode</span>;
[<span>CEReactions</span>, <span data-x="xattr-Reflect">Reflect</span>] attribute boolean <dfn attribute for="HTMLTemplateElement" data-x="dom-template-shadowrootdelegatesfocus">shadowRootDelegatesFocus</dfn>;
[<span>CEReactions</span>, <span data-x="xattr-Reflect">Reflect</span>] attribute boolean <dfn attribute for="HTMLTemplateElement" data-x="dom-template-shadowrootclonable">shadowRootClonable</dfn>;
Expand All @@ -67894,6 +67897,60 @@ interface <dfn interface>HTMLTemplateElement</dfn> : <span>HTMLElement</span> {

<p>In a rendering, the <code>template</code> element <span>represents</span> nothing.</p>

<p>The <dfn element-attr for="template"><code
data-x="attr-template-contentmethod">contentmethod</code></dfn> content attribute is an
<span>enumerated attribute</span> with the following keywords and states:</p>

<table>
<thead>
<tr>
<th>Keyword
<th>State
<th>Brief description
<tbody>
<tr>
<td><dfn attr-value for="template/contentmethod"><code data-x="attr-contentmethod-replace">replace</code></dfn>
<td><dfn data-x="attr-contentmethod-replace-state">Replace</dfn>
<td>Replace the target element itself.
<tr>
<td><dfn attr-value for="template/contentmethod"><code data-x="attr-contentmethod-replace-children">replace-children</code></dfn>
<td><dfn data-x="attr-contentmethod-replace-children-state">Replace Children</dfn>
<td>Replace the child nodes of the target element.
<tr>
<td><dfn attr-value for="template/contentmethod"><code data-x="attr-contentmethod-append">append</code></dfn>
<td><dfn data-x="attr-contentmethod-append-state">Append</dfn>
<td>Append child nodes to the target element.
<tr>
<td><dfn attr-value for="template/contentmethod"><code data-x="attr-contentmethod-prepend">prepend</code></dfn>
<td><dfn data-x="attr-contentmethod-prepend-state">Prepend</dfn>
<td>Prepend child nodes to the target element.
</table>

<p>The <code data-x="attr-template-contentmethod">contentmethod</code> attribute's <i
data-x="invalid value default">invalid value default</i> and <i data-x="missing value
default">missing value default</i> are both the <dfn
data-x="attr-contentmethod-none-state">None</dfn> state.</p>

<p>The <dfn element-attr for="htmlsvg-global"><code data-x="attr-contentname">contentname</code></dfn>
attribute value points to the target for template contentmethod, like an ID attribute.</p>
<!-- TODO better words, and should this be in another section since it's not for <template>? -->

<p>If specified, the <code data-x="attr-contentname">contentname</code> attribute value must equal
the <code data-x="attr-contentname">contentname</code> of another element in the same
<span>tree</span>.</p>
<!-- TODO: make this non-symmetrical and matching the processing model -->

<p>Each <code>template</code> element has an associated <dfn for="template">content target</dfn>
which is an element or null, initially null.</p>

<p>Each <code>template</code> element has an associated <dfn for="template">content prepend
target</dfn> which is an element or null, initially null.</p>

<p class="note">The <span>content target</span> element is used to adjust the parser's insertion
point based on the <code data-x="attr-template-contentmethod">contentmethod</code> attribute.
The <span>content prepend target</span> is used only for the
<span data-x="attr-contentmethod-prepend-state">Prepend</span> state.</p>

<p>The <dfn element-attr for="template"><code
data-x="attr-template-shadowrootmode">shadowrootmode</code></dfn> content attribute is an
<span>enumerated attribute</span> with the following keywords and states:</p>
Expand Down Expand Up @@ -68075,6 +68132,13 @@ interface <dfn interface>HTMLTemplateElement</dfn> : <span>HTMLElement</span> {
not a <code>ShadowRoot</code> node; otherwise null.</p>
</div>

<div algorithm>
<p>The <dfn attribute for="HTMLTemplateElement"><code
data-x="dom-template-contentmethod">contentMethod</code></dfn> IDL attribute must
<span>reflect</span> the <code data-x="attr-template-contentmethod">contentmethod</code> content
attribute, <span>limited to only known values</span>.</p>
</div>

<div algorithm>
<p>The <dfn attribute for="HTMLTemplateElement"><code
data-x="dom-template-shadowrootmode">shadowRootMode</code></dfn> IDL attribute must
Expand Down Expand Up @@ -139261,9 +139325,32 @@ dictionary <dfn dictionary>StorageEventInit</dfn> : <span>EventInit</span> {
</li>

<li>
<p>If the <var>adjusted insertion location</var> is inside a <code>template</code>
element, let it instead be inside the <code>template</code> element's <span>template
contents</span>, after its last child (if any).</p>
<p>If <var>adjusted insertion location</var> is inside a <code>template</code> element whose
<span>content target</span> is non-null:</p>

<ol>
<li><p>Let <var>target</var> be the <code>template</code> element's <span>content target</span>.</p></li>

<li><p>Let <var>state</var> be the state the <code>template</code> element's
<code data-x="attr-template-contentmethod">contentmethod</code> attribute is in.</p></li>

<li><p>Assert: <var>state</var> is not <span data-x="attr-contentmethod-none-state">None</span>.</p></li>

<li><p>If <var>state</var> is <span data-x="attr-contentmethod-replace-state">Replace</span>,
set <var>adjusted insertion location</var> to inside <var>target</var>'s parent element, after
<var>target</var>.</p></li>

<li><p>If <var>state</var> is <span data-x="attr-contentmethod-replace-children-state">Replace Children</span>,
set <var>adjusted insertion location</var> to inside <var>target</var>.</p></li>

<li><p>If <var>state</var> is <span data-x="attr-contentmethod-append-state">Append</span>,
set <var>adjusted insertion location</var> to inside <var>target</var>, after its last child
(if any).</p></li>

<li><p>If <var>state</var> is <span data-x="attr-contentmethod-prepend-state">Prepend</span>,
set <var>adjusted insertion location</var> to inside <var>target</var>, before the
<code>template</code> element's <span>content prepend target</span> (if any).</p></li>
</ol>
</li>

<li>
Expand Down Expand Up @@ -139413,6 +139500,53 @@ dictionary <dfn dictionary>StorageEventInit</dfn> : <span>EventInit</span> {
algorithm</span>, then push a new <span>element queue</span> onto <var>element</var>'s
<span>relevant agent</span>'s <span>custom element reactions stack</span>.</p></li>

<li>
<p>If <var>element</var> has a <code data-x="attr-contentname">contentname</code> attribute
specified and <var>adjusted insertion location</var> is inside a <code>template</code> element whose
<code data-x="attr-template-contentmethod">contentmethod</code> attribute is not in the <span
data-x="attr-contentmethod-none-state">None</span> state:</p>

<ol>
<li><p>Let <var>template</var> be <var>element</var>'s <span>parent</span>.</p></li>

<li><p>Assert: <var>template</var> is a <code>template</code> element.</p></li>

<li>
<p>Let <var>scope</var> be the <var>template</var>'s <span>parent</span>.</p>

<p class="note">The <code>template</code> element's parent will often be an element, but can
be a <code>DocumentFragment</code> in the <span>fragment case</span>.</p>
</li>

<li><p>If <var>scope</var> is a <code>body</code> element, set <var>scope</var> to its
parent.</p></li>

<li><p>Let <var>target</var> be the first element in <span>tree order</span> within
<var>scope</var> with a <code data-x="attr-contentname">contentname</code> attribute
value equal to that of <var>element</var>.</p></li>

<li><p>If <var>target</var> is null or if <var>target</var> doesn't have the same local name
and namespace as <var>element</var>, TODO and return.</p></li>

<li>
<p>Set <var>template</var>'s <span>content target</span> to <var>target</var>.</p>

<p class="note">The <span>content target</span> will be used later when nodes are to be inserted
into the child of the template element that has a contentname attribute.</p>
</li>

<li><p>Let <var>state</var> be the state that <var>template</var>'s
<code data-x="attr-template-contentmethod">contentmethod</code> attribute is in.</p></li>

<li><p>If <var>state</var> is <span data-x="attr-contentmethod-replace-state">Replace</span>,
remove <var>target</var> from its parent.</p></li>

<li><p>If <var>state</var> is <span data-x="attr-contentmethod-replace-children-state">Replace Children</span>,
remove <var>target</var>'s children from <var>target</var>.</p></li>
</ol>
<!-- Should we still insert the element in the following steps? Does it matter? -->
</li>

<li><p>Insert <var>element</var> at the <var>adjusted insertion location</var>.</p></li>

<li><p>If the parser was not created as part of the <span>HTML fragment parsing
Expand Down Expand Up @@ -140196,9 +140330,13 @@ document.body.appendChild(text);
<p>If any of the following are false:</p>

<ul>
<li><var>templateStartTag</var>'s <code
data-x="attr-template-contentmethod">contentmethod</code> is not in the <span
data-x="attr-contentmethod-none-state">None</span> state; or</li>

<li><var>templateStartTag</var>'s <code
data-x="attr-template-shadowrootmode">shadowrootmode</code> is not in the <span
data-x="attr-shadowrootmode-none-state">None</span> state;</li>
data-x="attr-shadowrootmode-none-state">None</span> state; or</li>

<li><var>document</var>'s <span
data-x="concept-document-allow-declarative-shadow-roots">allow declarative shadow
Expand All @@ -140208,11 +140346,13 @@ document.body.appendChild(text);
open elements</span>,</li>
</ul>

<p>then <span>insert an HTML element</span> for the token.</p>
<p>then <span>insert an HTML element</span> for the token and return.</p>
</li>

<li>
<p>Otherwise:</p>
<p>If <var>templateStartTag</var>'s <code
data-x="attr-template-shadowrootmode">shadowrootmode</code> is not in the <span
data-x="attr-shadowrootmode-none-state">None</span> state:</p>

<ol>
<li><p>Let <var>declarativeShadowHostElement</var> be <span>adjusted current
Expand Down Expand Up @@ -140289,6 +140429,17 @@ document.body.appendChild(text);
</li>
</ol>
</li>

<li>
<p>Otherwise, if <var>templateStartTag</var>'s <code
data-x="attr-template-contentmethod">contentmethod</code> is not in the <span
data-x="attr-contentmethod-none-state">None</span> state:</p>

<ol>
<li><p>TODO: what to we need to do so that elements are inserted into the template element
and redirected by our pre-insertion steps?</p></li>
</ol>
</li>
</ol>
</dd>

Expand Down Expand Up @@ -152714,6 +152865,19 @@ interface <dfn interface>External</dfn> {
<td> Whether the element is editable
<td> "<code data-x="">true</code>"; "<code data-x="">plaintext-only</code>";
"<code data-x="">false</code>"
<tr>
<th> <code data-x="">contentmethod</code>
<td> <code data-x="attr-template-contentmethod">template</code>
<td> Enables out-of-order streaming <!-- TODO better words -->
<td> "<code data-x="attr-contentmethod-replace">replace</code>";
"<code data-x="attr-contentmethod-replace-children">replace-children</code>";
"<code data-x="attr-contentmethod-append">append</code>";
"<code data-x="attr-contentmethod-prepend">prepend</code>"
<tr>
<th> <code data-x="">contentname</code>
<td> <span data-x="attr-contentname">HTML elements</span>
<td> Unique string to target what contentmethod affects <!-- TODO better words -->
<td> <a href="#attribute-text">Text</a>*
<tr>
<th> <code data-x="">controls</code>
<td> <code data-x="attr-media-controls">audio</code>;
Expand Down