[css-pseudo-4] Define painting of text-shadow for highlight pseudos. #3932

Author: fantasai

css-pseudo-4/Overview.bs

@@ -670,6 +670,9 @@ Cascading and Per-Element Highlight Styles</h3>
 <h3 id="highlight-painting">
 Painting the Highlight</h3>
 
+<h4 id="highlight-backgrounds">
+Backgrounds</h4>
+
   Each <a>highlight pseudo-element</a> draws its background
   over the corresponding portion of the <a>highlight overlay</a>,
   painting it
@@ -685,6 +688,22 @@ Painting the Highlight</h3>
   css/css-pseudo/highlight-z-index-002.html
   </wpt>
 
+<h4 id="highlight-shadows">
+Shadows</h4>
+
+  Any 'text-shadow' applying to a [=highlight pseudo-element=]
+  is drawn over its corresponding [=highlight overlay=] background.
+  Such text shadows also stack over each other
+  (and over any original 'text-shadow' applied to the text and its decorations,
+  which continues to apply).
+
+  Note: Since each [=highlight overlay=] background
+  is drawn over any shadows belonging to the layer(s) below,
+  a [=highlight overlay=] background can obscure lower-level shadows.
+
+<h4 id="highlight-text">
+Text and Text Decorations</h4>
+
   A <a>highlight pseudo-element</a>
   also suppresses the drawing of any selected text
   (and any text decorations applied to that text).
@@ -711,9 +730,8 @@ Painting the Highlight</h3>
   when that is not ''currentColor'',
   regardless of their original color or fill specifications.
 
-  Issue: What should happen with text shadows?
-  Drawing them in their original color is disconcerting if that color is not a shade of gray.
-  Maybe if the overlay has a background, suppress any text shadows below it?
+<h4 id="highlight-replaced">
+Replaced Elements</h4>
 
   For non-replaced content, the UA must honor the 'color' and 'background-color'
   (including their alpha channels) as specified.