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Introduce customelementregistry global attribute #12000

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Introduce customelementregistry global attribute #12000

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9879734
Introduce customelementregistry global attribute
Dec 8, 2025
ff894ae
Add keep element custom element registry null
Dec 9, 2025
767a181
Address PR review feedback for customelementregistry attribute
Apr 24, 2026
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40 changes: 38 additions & 2 deletions source
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Original file line number Diff line number Diff line change
Expand Up @@ -3438,6 +3438,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
<li><dfn data-x-href="https://dom.spec.whatwg.org/#valid-attribute-local-name">valid attribute local name</dfn></li>
<li><dfn data-x-href="https://dom.spec.whatwg.org/#valid-element-local-name">valid element local name</dfn></li>
<li><dfn data-x-href="https://dom.spec.whatwg.org/#is-a-global-custom-element-registry">is a global custom element registry</dfn></li>
<li><dfn data-x-href="https://dom.spec.whatwg.org/#concept-element-keep-custom-element-registry-null">keep element custom element registry null</dfn></li>
<li><dfn data-x-href="https://dom.spec.whatwg.org/#dom-processinginstruction-target" data-x="dom-ProcessingInstruction-target">processing instruction target</dfn></li>
</ul>

Expand Down Expand Up @@ -13028,6 +13029,7 @@ interface <dfn interface>HTMLElement</dfn> : <span>Element</span> {
[<span>CEReactions</span>, <span data-x="xattr-ReflectSetter">ReflectSetter</span>] attribute DOMString <span data-x="dom-writingSuggestions">writingSuggestions</span>;
[<span>CEReactions</span>, <span data-x="xattr-ReflectSetter">ReflectSetter</span>] attribute DOMString <span data-x="dom-autocapitalize">autocapitalize</span>;
[<span>CEReactions</span>] attribute boolean <span data-x="dom-autocorrect">autocorrect</span>;
[<span>CEReactions</span>, <span data-x="xattr-Reflect">Reflect</span>] attribute boolean <dfn attribute for="HTMLElement" data-x="dom-element-customElementRegistry">customElementRegistry</dfn>;

@annevk annevk Jun 26, 2026

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I'm not sure why we did not spot this before, but this clashes directly with https://dom.spec.whatwg.org/#dom-element-customelementregistry

@Jamesernator Jamesernator Jun 27, 2026

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Perhaps the attribute should be called something like initialcustomelementregistry, this would also make it clearer that setting the attribute has no effect on the actual customElementRegistry.

@ja-y-son ja-y-son Jun 29, 2026

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The attribute hasn't been out for too long so it's probably still not too late to change it. Perhaps mirroring what we have for shadowrootcustomelementregistry, we can make this attribute elementcustomelementregistry. @annevk @Jamesernator thoughts?

@keithamus keithamus Jul 1, 2026

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I'd prefer initialcustomelementregistry to elementcustomelementregistry. I kind of wonder if we could get away without the IDL reflection, though? It would be quite strange for the content attribute to not reflect, but maybe that's okay?

@annevk annevk Jul 1, 2026

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Since we've gone out of our way to reflect even the attributes on the template element that would be very weird and I don't think we should do that.

@annevk annevk Jul 9, 2026

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I discussed this with colleagues and we're not sure about either initial or default as the registry in principle doesn't change. How about scopedcustomelementregistry with scopedCustomElementRegistry as the IDL member?

@ja-y-son ja-y-son Jul 9, 2026

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I have mixed feelings about scopedcustomelementregistry because having this attribute does not mean the user cannot assign a global registry to it later on, but perhaps that's not really a concern. I'm okay with this option, though I'm still more favoring elementcustomelementregistry because it has almost identical capabilities as shadowrootcustomelementregistry but on elements, so the naming mirroring can also make sense.


[<span>CEReactions</span>] attribute [<span>LegacyNullToEmptyString</span>] DOMString <span data-x="dom-innerText">innerText</span>;
[<span>CEReactions</span>] attribute [<span>LegacyNullToEmptyString</span>] DOMString <span data-x="dom-outerText">outerText</span>;
Expand Down Expand Up @@ -14375,6 +14377,7 @@ 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-customelementregistry">customelementregistry</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 @@ -78747,6 +78750,14 @@ console.assert(el instanceof SpiderMan); // upgraded!</code></pre>
<code>CustomElementRegistry</code> object, it intentionally cannot be changed any further. This
simplifies reasoning about code and allows implementations to optimize.</p>

<h4>The <code data-x="attr-customelementregistry">customelementregistry</code> attribute</h4>

<p> The
<dfn element-attr for="html-global"><code data-x="attr-customelementregistry">customelementregistry</code></dfn>
attribute is used to specify whether the parser should be
<span data-x="look up a custom element registry">looking up a custom element registry</span>
when the parser runs <span>Create an element for the token</span>. The value is boolean.</p>


<h4><dfn data-x="custom-element-upgrades">Upgrades</dfn></h4>

Expand Down Expand Up @@ -144196,8 +144207,15 @@ dictionary <dfn dictionary>StorageEventInit</dfn> : <span>EventInit</span> {
<li><p>Let <var>is</var> be the value of the "<code data-x="attr-is">is</code>" attribute in
<var>token</var>, if such an attribute exists; otherwise null.</p></li>

<li><p>Let <var>registry</var> be the result of <span data-x="look up a custom element
registry">looking up a custom element registry</span> given <var>intendedParent</var>.</p></li>
<li><p>Let <var>registry</var> be null if
<code data-x="attr-customelementregistry">customelementregistry</code> attribute exists;
otherwise let <var>registry</var> be the result of
<span data-x="look up a custom element registry">looking up a custom element registry</span>
given <var>intendedParent</var>.</p></li>
Comment thread
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<li><p>Let <var>keepRegistryNull</var> be true if
<code data-x="attr-customelementregistry">customelementregistry</code> attribute exists;
otherwise false.

<li><p>Let <var>definition</var> be the result of <span data-x="look up a custom element
definition">looking up a custom element definition</span> given <var>registry</var>,
Expand Down Expand Up @@ -144286,6 +144304,10 @@ dictionary <dfn dictionary>StorageEventInit</dfn> : <span>EventInit</span> {
with the <code>form</code> element pointed to by the <span><code data-x="">form</code> element
pointer</span> and set <var>element</var>'s <span>parser inserted flag</span>.</p></li>

<li><p>If <var>keepRegistryNull</var> is true, set <var>element</var>'s
<span>keep element custom element registry null</span>
to true.

<li><p>Return <var>element</var>.</p></li>
</ol>
</div>
Expand Down Expand Up @@ -149032,6 +149054,15 @@ document.body.appendChild(text);
data-x="escaping a string">escaped as described below</span> in <i>attribute mode</i>,
followed by a U+0022 QUOTATION MARK character (&quot;).</p>

<p>If the element does not have a
<code data-x="attr-customelementregistry">customelementregistry</code> attribute in its
attribute list, and <var>current node</var>'s
<span data-x="element-custom-element-registry">custom element registry</span> is not the
same as the result of
<span data-x="look up a custom element registry">looking up a custom element
registry</span> given <var>current node</var>'s parent element, then append
"<code data-x=""> customelementregistry=&quot;&quot;</code>".</p>

<p>For each attribute that the element has, append a U+0020 SPACE character, the <span
data-x="attribute's serialized name">attribute's serialized name as described below</span>, a
U+003D EQUALS SIGN character (=), a U+0022 QUOTATION MARK character (&quot;), the
Expand Down Expand Up @@ -157786,6 +157817,11 @@ interface <dfn interface>External</dfn> {
<td> "<code data-x="attr-crossorigin-anonymous-keyword">anonymous</code>";
"<code data-x="attr-crossorigin-use-credentials-keyword">use-credentials</code>";
the empty string
<tr>
<th> <code data-x="">customelementregistry</code>
<td> <span data-x="attr-class">HTML elements</span>
<td> Whether the element should use scoped custom element registry
<td> <span>Boolean attribute</span>
<tr>
<th> <code data-x="">data</code>
<td> <code data-x="attr-object-data">object</code>
Expand Down
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