[css-text-decor-3] Clarifications to line position rules.

Author: fantasai

css-text-decor-3/Overview.html

@@ -971,37 +971,39 @@ <h3 id=line-position><span class=secno>2.7. </span> Determining the
    Position and Thickness of Line Decorations</h3>
 
   <p>In determining the position of text decoration lines, user agents must
-   first determine, per line, an "ideal" position for every fragment of a
-   single <a href="#decorating-box"><i>decorating box</i></a>, then position
-   the decoration as follows:
+   consider, per line box, the "ideal" positions of all fragments of in-flow
+   inline descendants of the <a href="#decorating-box"><i>decorating
+   box</i></a> on that line as follows:
 
   <dl>
    <dt>overlines (and <i>over</i>-positioned underlines)
 
-   <dd> Position the line with respect to the highest <i>over</i> content
-    edge of the decorated fragments.
+   <dd> Align the line decoration with respect to the highest
+    <i>text-over</i> edge of the considered fragments.
 
    <dt><a href="#alphabetic"><i>alphabetic</i></a> underlines
 
-   <dd> Position the line to an average of the ideal underlines of the
-    decorated fragments, assigning any fragment with non-initial ‘<code
+   <dd> Align the line decoration to an average of the ideal underlines of
+    the considered fragments, assigning any inline with non-initial ‘<code
     class=property>vertical-align</code>’ the ideal position of its parent,
-    but below the lowest alphabetic baseline considered.
+    but keeping the line decoration below the lowest alphabetic baseline
+    considered. (A considered alphabetic baseline can be above the averaged
+    position if the dominant baseline is non-alphabetic.)
 
    <dt>non-alphabetic underlines (and <a
     href="#under"><i>under</i></a>-positioned overlines)
 
-   <dd> Position the line with respect to the lowest <a
-    href="#under"><i>under</i></a> content edge of the decorated fragments.
+   <dd> Position the line decoration with respect to the lowest
+    <i>text-under</i> edge of the considered fragments.
 
    <dt>line-throughs
 
-   <dd> For each set of decorated fragments with the same ‘<code
+   <dd> For each set of considered fragments with the same ‘<code
     class=property>font-size</code>’, compute an ideal position averaged
     from their direct contents and font metrics, assigning any fragment with
-    non-initial ‘<code class=property>vertical-align</code>’the ideal
+    non-initial ‘<code class=property>vertical-align</code>’ the ideal
     position of its parent. Position the portion of the line across each
-    decorated fragment at the fragment's ideal position. (Essentially, this
+    decorated fragment at that fragment's ideal position. (Essentially, this
     performs the same sort of averaging as for alphabetic underlines, but
     recomputes the position when drawing across a descendant with a different
     computed ‘<code class=property>font-size</code>’.) <span
@@ -1853,7 +1855,7 @@ <h3 class=no-num id=recent-changes> Changes since the <a
    <li>Clarified and corrected the definitions for <a
     href="#line-decoration">line decoration propagation</a>
 
-   <li>Changed the definitions for averaging <a href="#line-positions">line
+   <li>Changed the definitions for averaging <a href="#line-position">line
     decoration positions</a> to better accommodate changes in font size.
 
    <li>Changed ‘<code class=css>above</code>’ and ‘<code

css-text-decor-3/Overview.src.html

@@ -636,31 +636,34 @@ <h3 id="line-position">
 Determining the Position and Thickness of Line Decorations</h3>
 
   <p>In determining the position of text decoration lines,
-    user agents must first determine, per line,
-    an "ideal" position for every fragment of a single <i>decorating box</i>,
-    then position the decoration as follows:
+    user agents must consider, per line box, the "ideal" positions of all fragments
+    of in-flow inline descendants of the <i>decorating box</i> on that line
+    as follows:
 
   <dl>
     <dt>overlines (and <i>over</i>-positioned underlines)
     <dd>
-      Position the line with respect to the highest <i>over</i> content edge of the decorated fragments.
+      Align the line decoration with respect to the highest
+      <i>text-over</i> edge of the considered fragments.
 
     <dt><i>alphabetic</i> underlines
     <dd>
-      Position the line to an average of the ideal underlines of the decorated fragments,
-      assigning any fragment with non-initial 'vertical-align' the ideal position of its parent,
-      but below the lowest alphabetic baseline considered.
+      Align the line decoration to an average of the ideal underlines of the considered fragments,
+      assigning any inline with non-initial 'vertical-align' the ideal position of its parent,
+      but keeping the line decoration below the lowest alphabetic baseline considered.
+      (A considered alphabetic baseline can be above the averaged position if the dominant baseline is non-alphabetic.)
 
     <dt>non-alphabetic underlines (and <i>under</i>-positioned overlines)
     <dd>
-      Position the line with respect to the lowest <i>under</i> content edge of the decorated fragments.
+      Position the line decoration with respect to the lowest
+      <i>text-under</i> edge of the considered fragments.
 
     <dt>line-throughs
     <dd>
-      For each set of decorated fragments with the same 'font-size', 
+      For each set of considered fragments with the same 'font-size', 
       compute an ideal position averaged from their direct contents and font metrics,
-      assigning any fragment with non-initial 'vertical-align'the ideal position of its parent.
-      Position the portion of the line across each decorated fragment at the fragment's ideal position.
+      assigning any fragment with non-initial 'vertical-align' the ideal position of its parent.
+      Position the portion of the line across each decorated fragment at that fragment's ideal position.
       (Essentially, this performs the same sort of averaging as for alphabetic underlines,
       but recomputes the position when drawing across a descendant with a different computed 'font-size'.)
       <span class="issue">Need an example here</span>
@@ -1270,7 +1273,7 @@ <h3 class="no-num" id="recent-changes">
   <ul>
     <li>Changed line decorations to not skip margins/padding/borders of descendents' inline boxes.
     <li>Clarified and corrected the definitions for <a href="#line-decoration">line decoration propagation</a>
-    <li>Changed the definitions for averaging <a href="#line-positions">line decoration positions</a>
+    <li>Changed the definitions for averaging <a href="#line-position">line decoration positions</a>
         to better accommodate changes in font size.
     <li>Changed ''above'' and ''below'' values of 'text-emphasis-position' and 'text-underline-position'
         to ''over'' and ''under'' to match terminology in 'text-decoration-line'.