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[css-scoping-1] add :has-slotted() pseudo class #10586

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[css-scoping-1] add :has-slotted() pseudo class #10586

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303ff0d
add has-slotted psuedo class
keithamus Jul 17, 2024
f4afce1
fix typo
keithamus Aug 20, 2024
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42 changes: 40 additions & 2 deletions css-scoping-1/Overview.bs
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Expand Up @@ -424,6 +424,44 @@ Selecting Slot-Assigned Content: the ''::slotted()'' pseudo-element</h4>
The only way to style assigned text nodes
is by styling the <a>slot</a> and relying on inheritance.

<h4 id='has-slotted-pseudo'>
Matching Selectors Against Slot-Assigned Content: the '':has-slotted()'' pseudo-class</h4>

The <dfn selector>:has-slotted()</dfn> pseudo-class, when evaluated
<a>in the context of a shadow tree</a>,
matches the <a>slot</a>, if one of its
<a lt="find flattened slottables">assigned elements, after flattening,</a> matches the provided <<compound-selector>>.
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"after flattening" is interesting here because it give "non-slotted" content while being required to gather all slotted content. E.G.:

<div>
  <template shadowrootmode="open">
    <style>
      div {
        color: green;
      }
      :has-slotted(div) {
        color: red;
      }
    </style>
    <slot><div>Test</div></slot>
  </template>
</div>

In the example above "Test" will display red in the case that flattened elements are leveraged.

However, if you don't use flattened elements:

<div>
  <template shadowrootmode="open">
    <div>
      <template shadowrootmode="open">
        <style>
          div {
            color: green;
          }
          :has-slotted(div) {
            color: red;
          }
        </style>
        <slot></slot>
      </template>
      <slot><div>Test</div></slot>
    </div>
  </template>
</div>

This "Test" will also be red. And, without flattened elements,

<div>
  <template shadowrootmode="open">
    <div>
      <template shadowrootmode="open">
        <style>
          div {
            color: green;
          }
          :has-slotted(div) {
            color: red;
          }
        </style>
        <slot></slot>
      </template>
      <div>Test</div>
    </div>
  </template>
</div>

This "Test" will also be red.

I'm not sure it's a real thing, but is there a place between ::slotted(*) and .assignedElements({flatten: true}) that would resolve the external assigned to a slot and not the default ones internal to the shadow host?

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For consistency, I think it's important that :has-slotted matches using the same rules for matchable elements as ::slotted.

Concretely, since ::slotted() never matches either <slot> or fallback content, :has-slotted also should not match when it would by selecting either <slot> or fallback content.

See #5482. IMO, the spec is still very confusing and possibly indicates that this should match, but the CSS working group resolved that the current behavior is intended in #5482.

I think matching against fallback content both for ::slotted and :has-slotted is valuable, but I suggest it should be tackled as a follow-on to this feature.

In any other context, it matches nothing. This pseudo-class only exists on <a>slots</a>.

The [=specificity=] of '':has-slotted()'' is that of a pseudo-class,
plus the [=specificity=] of its argument.

The grammar of the '':has-slotted()'' pseudo-element is:

<pre class=prod>:has-slotted( <<compound-selector>> )</pre>

<div class="example">
For example, say you had a component with both children and a shadow tree,
like the following:

<pre>
&lt;x-foo>
&lt;div id="one" slot="foo" class="foo">...&lt;/div>
&lt;"shadow tree">
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Do you want to use the <::shadow> markup here?

&lt;slot id="theslot" name="foo">&lt;/slot>
&lt;/"shadow tree">
&lt;/x-foo>
</pre>

For a stylesheet within the <a>shadow tree</a>,
selectors like '':has-slotted(*)'', '':has-slotted(div)'', '':has-slotted(.foo)'', and '':has-slotted(#one)''
will match ''#theslot'', while '':has-slotted(p)'', '':has-slotted(:not(.foo))'', '':has-slotted(#two)''
will not.
</div>

Note: '':has-slotted()'' will only match the ''slot'' element, not the contents. Slotted contents
can be matched with the ''::slotted()'' pseudo-element.

<!--
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Expand Down Expand Up @@ -613,7 +651,7 @@ Name-Defining Constructs and Inheritance</h3>

For example,
given the following document
(using the imaginary <::shadow></::shadow> markup
(using the imaginary ''<::shadow></::shadow>'' markup
to indicate an element's [=shadow tree=]):

<xmp highlight=markup>
Expand Down Expand Up @@ -733,7 +771,7 @@ Serialized Tree-Scoped References</h4>

For example,
given the following document
(using the imaginary <::shadow></::shadow> markup
(using the imaginary ''<::shadow></::shadow>'' markup
to indicate an element's [=shadow tree=]):

<xmp highlight=markup>
Expand Down