rewrite and heavily simplify paired cascade text

delan · delan · commit 86bb487445f1 · 2022-04-15T15:54:12.000+08:00
diff --git a/css-pseudo-4/Overview.bs b/css-pseudo-4/Overview.bs
@@ -696,12 +696,11 @@ Styling Highlights</h3>
 
   Issue: Are there any other properties that should be included here?
 
-  In particular,
-  'color' and 'background-color' are known as <dfn>highlight colors</dfn>,
-  and their [=used values=] are handled specially (see [[#paired-cascade]]).
+  'color' and 'background-color'
+  are known as <dfn>highlight colors</dfn>.
   Because this concept exists for compatibility reasons,
   other similar properties
-  like 'fill-color'
+  like 'fill-color' or 'stroke-color'
   must not be treated as highlight colors.
 
 <!-- Add this back if for some reason someone wants to implement 'outline'?
@@ -716,7 +715,7 @@ Styling Highlights</h3>
 -->
 
   Note: Historically (and at the time of writing)
-  only the [=highlight colors=] have been interoperably supported.
+  only the highlight colors have been interoperably supported.
 
 <h3 id=highlight-ua-styles>
 Default UA Styles</h3>
@@ -894,44 +893,39 @@ Painting the Highlight</h3>
 <h4 id="paired-cascade">
 Highlight Colors</h4>
 
-  With the exception of ''revert'' (see below),
+  For compatibility reasons,
   [=default highlight colors=]
-  for a given [=highlight pseudo-element=]
   must only be [=used value|used=]
-  instead of [=initial values=]
-  when neither the originating element’s [=cascade=],
-  nor those of any of the originating element’s ancestors,
-  yield any highlight colors
+  when neither of the [=highlight colors=]
+  yield a [=cascaded value=]
+  or [=specified value=]
   of the [=author origin=].
-  In other words,
-  when the author sets one “custom” highlight color,
-  defaults for the other highlight color are suppressed.
-
-  Note: 'stroke-color' and 'fill-color' have their usual effects
-  on the foreground color,
-  but unlike 'color',
-  they do not suppress the default 'background-color'.
-
-  When a highlight color is ''revert'',
-  [=default highlight colors=] are suppressed
-  if and only if the cascade is “rolled back”
-  to one of the origins listed above.
-  For example,
-  ''revert'' in an [=author-origin=] rule
-  rolls back the cascade to the [=user origin=],
-  so defaults are not suppressed.
-
-  Note: all other explicit defaults,
-  including ''unset'',
-  suppress [=default highlight colors=] like any ordinary value.
-  This happens to be consistent with
-  how [=explicit defaulting=] is defined:
-  it affects [=specified values=]
-  based on [=cascaded values=].
-  Even though the outcome is <em>as if</em>
-  the [=cascade=] was modified in some way,
-  the [=cascade=] is already done,
-  so they exist unchanged as [=cascaded values=].
+  When a highlight color is ''revert'' or ''revert-layer'',
+  the origin <em>after</em> rolling back the cascade
+  determines whether this is the case.
+
+  <div class="example">
+    For example,
+    given the following markup:
+    <pre class="lang-markup">
+      &lt;p>Highlight this &lt;em>and this&lt;/em>.&lt;/p>
+    </pre>
+    Any of the following rules
+    would suppress the default 'background-color'
+    for ''::selection''
+    in the <code>&lt;em></code> element
+    if given by the author:
+    <pre class="lang-css">
+      /* cascaded value is author origin */
+      em::selection { color: initial; }
+      em::selection { color: inherit; }
+      em::selection { color: unset; }
+      em::selection { color: green; }
+
+      /* specified value is author origin */
+      p::selection { color: green; }
+    </pre>
+  </div>
 
 <h4 id="highlight-backgrounds">
 Backgrounds</h4>
