[css-shadow-parts] Switch ::theme() to keying off of a theme='' attribute. Fixes w3c#1972.

Author: tabatkins

css-shadow-parts/Overview.bs

@@ -13,9 +13,11 @@ Abstract: This specification defines the ''::part()'' and ''::theme()'' pseudo-e
 <pre class=link-defaults>
 spec:selectors-4;
     type:selector; text::hover
-    type:dfn; text:dynamic profile
+    type:dfn; text:live profile
     type:dfn; text:structural pseudo-class
 spec:dom; type:dfn; for:/; text:shadow root
+spec:infra;
+    type:dfn; text:string
 </pre>
 
 Introduction {#intro}
@@ -62,7 +64,7 @@ it exposed too much of a component's internal structure to scrutiny,
 defeating some of the encapsulation benefits that using Shadow DOM brings.
 For this,
 and other performance-related reasons,
-the >>> combinator was eventually removed from the <a>dynamic profile</a>.
+the >>> combinator was eventually removed from the <a>live profile</a>.
 
 This left us with using <a>custom properties</a> as the only way to style into a shadow tree:
 the component would advertise that it uses certain <a>custom properties</a> to style its internals,
@@ -112,7 +114,7 @@ for something authors can already do with <a>custom properties</a>.
 By separating out the explicitly "published" parts of an element
 (the <a>shadow part map</a>
 from the sub-parts that it merely happens to contain
-(the <a>shadow theme map</a>,
+(the <a>computed shadow theme map</a>,
 it also helps with encapsulation,
 as authors can use ''::part()'' without fear of accidental over-styling.
 
@@ -153,20 +155,33 @@ The "part name" should be considered similar to a class,
 not an id or tagname.
 
 Each <a>shadow root</a> has a <dfn export for="shadow root">shadow part map</dfn>
-and a <dfn export for="shadow root">shadow theme map</dfn>,
-both of which are <a>ordered maps</a>.
+which is an <a>ordered map</a>,
+with keys that are [=strings=]
+and values that are [=ordered sets=] of elements.
 
 The <a>shadow part map</a> contains all the entries described by the elements in its <a>shadow tree</a>,
 as described above.
 
-If the <a>shadow root</a>'s {{ShadowRoot/mode}} is {{ShadowRootMode/"closed"}},
-the <a>shadow theme map</a> is identical to the <a>shadow part map</a>.
+Exposing More Widely: the <{html-global/theme}> attribute {#theme-attr}
+-----------------------------------------------------------------------
+
+In addition to the [=shadow part map=],
+every [=shadow root=] has a <dfn export for="shadow root">partial shadow theme map</dfn>
+and a <dfn export for="shadow root">computed shadow theme map</dfn>
+both of which are [=ordered maps=]
+(with the same key/value shape as the [=shadow part map=]),
+and the elements in the [=shadow tree=]
+have a corresponding <dfn element-attr for=html-global>theme</dfn> attribute.
+
+The <{html-global/theme}> attribute is parsed and interpreted identically to the <{html-global/part}> attribute,
+except that it adds its entries to the [=shadow root’s=] [=partial shadow theme map=] instead.
+
+If the [=shadow root’s=] {{ShadowRoot/mode}} is {{ShadowRootMode/"closed"}},
+the [=computed shadow theme map=] is identical to the [=partial shadow theme map=].
 Otherwise,
-it's the concatenation of the <a>shadow part map</a>
-with the <a>shadow theme maps</a> of every <a>shadow host</a>'s <a>shadow root</a> in its <a>shadow tree</a>.
+it's the union of the [=partial shadow theme map=]
+with the [=computed shadow theme maps=] of every [=shadow host’s=] [=shadow root=] in its [=shadow tree=].
 
-Issue: TODO: Define a syntax or new attribute
-to prevent an element from adding things to its <a>shadow root's</a> <a>shadow theme map</a>.
 
 Selecting a Shadow Element: the ''::part()'' and ''::theme()'' pseudo-elements {#part-theme}
 ============================================================================================
@@ -201,7 +216,7 @@ The ''::theme()'' pseudo-element is similar,
 except it can match regardless of whether the <a>originating element</a>
 is a <a>shadow host</a> or not.
 It matches the elements keyed to the specified <<ident>>
-in the <a>shadow theme map</a> of the <a>shadow trees</a>
+in the <a>computed shadow theme map</a> of the <a>shadow trees</a>
 of the <a>originating element</a> or any descendants.
 
 <div class="example">