[css-text-decor] Switch to talking about 'considered text'. Add issue about line-through positioning, especially in elements without text.

Author: tabatkins

css-text-decor/Overview.html

@@ -1043,59 +1043,85 @@ <h3 id=text-underline-position-property><span class=secno>2.6. </span> Text
 
   <h3 id=line-position><span class=secno>2.7. </span> Determining the
    Position and Thickness of Line Decorations</h3>
+  <!--
+  <p>Since line decorations can span elements with varying font sizes and
+    vertical alignments, the best position for a line decoration is not
+    necessarily the ideal position dictated by the <i>decorating box</i>.
+    In determining the position of text decoration lines within a given line box,
+    user agents must consider, for each <i>decorating box</i> on that line,
+    the “ideal” positions of such line decorations of each
+    run of text decorated by that <i>decorating box</i>
+    (each <dfn>considered run</dfn>).
+    However, descendants of the <i>decorating box</i>
+    that are skipped due to 'text-decoration-skip',
+    descendant inlines with ''text-decoration-skip: ink'',
+    and any descendants that do not participate in the <i>decorating box</i>’s inline formatting context
+    are excluded from the set of <i>considered fragments</i>.
+
+  <p>
+    <dfn>Decoration-affecting text</dfn> is any text decorated by a <i>decorating box</i>
+    that can affect the size and position of the decoration;
+    descendants that are skipped due to 'text-decoration-skip',
+    descendant inlines with ''text-decoration-skip: ink'',
+    and any descendants that do not participate in the <i>decorating box</i>’s inline formatting context
+    are not <i>considered fragments</i>.
+    The position and thickness of decorations on <i>considered fragments</i> are calculated by looking at sets of <i>considered fragments</i>:
+    each set is composed of all the <i>considered fragments</i> in a single line box 
+    and decorated by the same <i>decorating box</i>.
+-->
 
   <p>Since line decorations can span elements with varying font sizes and
    vertical alignments, the best position for a line decoration is not
    necessarily the ideal position dictated by the <a
    href="#decorating-box"><i>decorating box</i></a>. Instead, it's
    calculated, per line, from all text decorated by the <a
-   href="#decorating-box"><i>decorating box</i></a> on that line, the
-   <i>considered text</i>. However, descendants of the <a
+   href="#decorating-box"><i>decorating box</i></a> on that line, the <dfn
+   id=considered-text>considered text</dfn>. However, descendants of the <a
    href="#decorating-box"><i>decorating box</i></a> that are skipped due to
    ‘<a href="#text-decoration-skip"><code
    class=property>text-decoration-skip</code></a>’, descendant inlines with
    ‘<code class=css>text-decoration-skip: ink</code>’, and any
    descendants that do not participate in the <a
    href="#decorating-box"><i>decorating box</i></a>’s inline formatting
-   context are excluded from the set of <i>considered text</i>.
+   context are excluded from the set of <a
+   href="#considered-text"><i>considered text</i></a>.
 
-  <p> The line decoration positions are then calculated per set of
-   <i>considered fragments</i> as follows (treating <a
-   href="#underline-left"><i>over</i>-positioned underlines</a> as
-   <i>over</i> lines and <a href="#underline-left"><i>under</i>-positioned
+  <p> The line decoration positions are then calculated per line as follows
+   (treating <a href="#underline-left"><i>over</i>-positioned underlines</a>
+   as <i>over</i> lines and <a href="#underline-left"><i>under</i>-positioned
    overlines</a> as <i>under</i> lines):
 
   <dl>
-   <dt><a
-    href="http://www.w3.org/TR/css3-writing-modes/#over"><i>over</i></a>
+   <dt><a href="http://www.w3.org/TR/css-writing-modes/#over"><i>over</i></a>
     lines
 
    <dd> Align the line decoration with respect to the highest
     <!-- <i>text-over</i> baseline of the considered fragments. --> <a
-    href="http://www.w3.org/TR/css3-writing-modes/#over"><i>over</i></a> edge
-    of the <i>considered fragments</i>’ content boxes.
+    href="http://www.w3.org/TR/css-writing-modes/#over"><i>over</i></a>
+    EM-box edge of the <a href="#considered-text"><i>considered text</i></a>.
 
    <dt><a href="#underline-alphabetic"><i>alphabetic</i></a> underlines
 
    <dd>
     <p>The alphabetic underline position is calculated by taking the ideal
-     offset (from the alphabetic baseline) of each <i>considered
-     fragment</i>, averaging those, and then using the lowest alphabetic
-     baseline to actually position the line. (Alphabetic baselines can differ
-     between ‘<code class=css>baseline</code>’-aligned boxes if the
-     dominant baseline is non-alphabetic.) To prevent superscripts and
-     subscripts from throwing this position off-kilter, an inline with a
-     non-initial computed ‘<code class=property>vertical-align</code>’ is
-     treated as having the ideal underline position of their parent.
+     offset (from the alphabetic baseline) of each run of <a
+     href="#considered-text"><i>considered text</i></a>, averaging those, and
+     then using the lowest alphabetic baseline to actually position the line.
+     (Alphabetic baselines can differ between ‘<code
+     class=css>baseline</code>’-aligned boxes if the dominant baseline is
+     non-alphabetic.) To prevent superscripts and subscripts from throwing
+     this position off-kilter, an inline with a non-initial computed ‘<code
+     class=property>vertical-align</code>’ is treated as having the ideal
+     underline position of its parent.
 
    <dt>non-alphabetic <a
-    href="http://www.w3.org/TR/css3-writing-modes/#under"><i>under</i></a>
+    href="http://www.w3.org/TR/css-writing-modes/#under"><i>under</i></a>
     lines
 
    <dd> Position the line decoration with respect to the lowest
     <!-- <i>text-under</i> baseline of the considered fragments. --> <a
-    href="http://www.w3.org/TR/css3-writing-modes/#under"><i>under</i></a>
-    edge of the <i>considered fragments</i>’ content boxes.
+    href="http://www.w3.org/TR/css-writing-modes/#under"><i>under</i></a>
+    EM-box edge of the <a href="#considered-text"><i>considered text</i></a>.
 
    <dt>line-throughs
 
@@ -1104,12 +1130,20 @@ <h3 id=line-position><span class=secno>2.7. </span> Determining the
     descendant with a different computed ‘<code
     class=property>font-size</code>’. (This ensures that the text remains
     effectively “crossed out” despite any font size changes.) For each
-    set of <i>considered fragments</i> 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
-    position of its parent). Position the portion of the line across each
-    decorated fragment at that position.
+    run of <a href="#considered-text"><i>considered text</i></a> with the
+    same ‘<code class=property>font-size</code>’, compute an ideal
+    position averaged from its font metrics. To prevent superscripts and
+    subscripts from throwing this position off-kilter, an inline with a
+    non-initial computed ‘<code class=property>vertical-align</code>’ is
+    treated as having the ideal underline position of its parent. Position
+    the portion of the line across each decorated fragment at that position.
+    <p class=issue> For simplicity, line-throughs should draw over each
+     element at that element's preferred/averaged position. This can produce
+     some undesirable jumpiness, but there doesn't appear to be any way to
+     avoid that which is correct in all instances, and all attempts are
+     worryingly complex. What position should line-throughts adopt over
+     elements that have a different font-size, but no <a
+     href="#considered-text"><i>considered text</i></a>?
   </dl>
 
   <p> CSS does not define the thickness of line decorations. In determining

css-text-decor/Overview.src.html

@@ -683,12 +683,37 @@ <h3 id="text-underline-position-property">
 
 <h3 id="line-position">
 Determining the Position and Thickness of Line Decorations</h3>
+<!--
+  <p>Since line decorations can span elements with varying font sizes and
+    vertical alignments, the best position for a line decoration is not
+    necessarily the ideal position dictated by the <i>decorating box</i>.
+    In determining the position of text decoration lines within a given line box,
+    user agents must consider, for each <i>decorating box</i> on that line,
+    the “ideal” positions of such line decorations of each
+    run of text decorated by that <i>decorating box</i>
+    (each <dfn>considered run</dfn>).
+    However, descendants of the <i>decorating box</i>
+    that are skipped due to 'text-decoration-skip',
+    descendant inlines with ''text-decoration-skip: ink'',
+    and any descendants that do not participate in the <i>decorating box</i>’s inline formatting context
+    are excluded from the set of <i>considered fragments</i>.
 
+  <p>
+    <dfn>Decoration-affecting text</dfn> is any text decorated by a <i>decorating box</i>
+    that can affect the size and position of the decoration;
+    descendants that are skipped due to 'text-decoration-skip',
+    descendant inlines with ''text-decoration-skip: ink'',
+    and any descendants that do not participate in the <i>decorating box</i>’s inline formatting context
+    are not <i>considered fragments</i>.
+    The position and thickness of decorations on <i>considered fragments</i> are calculated by looking at sets of <i>considered fragments</i>:
+    each set is composed of all the <i>considered fragments</i> in a single line box 
+    and decorated by the same <i>decorating box</i>.
+-->
   <p>Since line decorations can span elements with varying font sizes and
     vertical alignments, the best position for a line decoration is not
     necessarily the ideal position dictated by the <i>decorating box</i>.
     Instead, it's calculated, per line, from all text decorated by the <i>decorating box</i> on that line,
-    the <i>considered text</i>.
+    the <dfn>considered text</dfn>.
     However, descendants of the <i>decorating box</i>
     that are skipped due to 'text-decoration-skip',
     descendant inlines with ''text-decoration-skip: ink'',
@@ -697,46 +722,56 @@ <h3 id="line-position">
 
   <p>
     The line decoration positions are then calculated
-    per set of <i>considered fragments</i>
+    per line
     as follows
     (treating <a href="#underline-left"><i>over</i>-positioned underlines</a> as <i>over</i> lines
     and <a href="#underline-left"><i>under</i>-positioned overlines</a> as <i>under</i> lines):
 
   <dl>
-    <dt><a href="http://www.w3.org/TR/css3-writing-modes/#over"><i>over</i></a> lines
+    <dt><a href="http://www.w3.org/TR/css-writing-modes/#over"><i>over</i></a> lines
     <dd>
       Align the line decoration with respect to the highest
       <!-- <i>text-over</i> baseline of the considered fragments. -->
-      <a href="http://www.w3.org/TR/css3-writing-modes/#over"><i>over</i></a> edge
-      of the <i>considered fragments</i>’ content boxes.
+      <a href="http://www.w3.org/TR/css-writing-modes/#over"><i>over</i></a> EM-box edge
+      of the <i>considered text</i>.
 
     <dt><a href="#underline-alphabetic"><i>alphabetic</i></a> underlines
     <dd>
       <p>The alphabetic underline position is calculated by taking
-      the ideal offset (from the alphabetic baseline) of each <i>considered fragment</i>,
+      the ideal offset (from the alphabetic baseline) of each run of <i>considered text</i>,
       averaging those, and then using the lowest alphabetic baseline to actually position the line.
       (Alphabetic baselines can differ between ''baseline''-aligned boxes
        if the dominant baseline is non-alphabetic.)
       To prevent superscripts and subscripts from throwing this position off-kilter,
       an inline with a non-initial computed 'vertical-align'
-      is treated as having the ideal underline position of their parent.
+      is treated as having the ideal underline position of its parent.
 
-    <dt>non-alphabetic <a href="http://www.w3.org/TR/css3-writing-modes/#under"><i>under</i></a> lines
+    <dt>non-alphabetic <a href="http://www.w3.org/TR/css-writing-modes/#under"><i>under</i></a> lines
     <dd>
       Position the line decoration with respect to the lowest
       <!-- <i>text-under</i> baseline of the considered fragments. -->
-      <a href="http://www.w3.org/TR/css3-writing-modes/#under"><i>under</i></a> edge
-      of the <i>considered fragments</i>’ content boxes.
+      <a href="http://www.w3.org/TR/css-writing-modes/#under"><i>under</i></a> EM-box edge
+      of the <i>considered text</i>.
 
     <dt>line-throughs
     <dd>
       Line-throughs essentially use the same sort of averaging as for alphabetic underlines,
       but recompute the position when drawing across a descendant with a different computed 'font-size'.
       (This ensures that the text remains effectively “crossed out” despite any font size changes.)
-      For each set of <i>considered fragments</i> 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).
+      For each run of <i>considered text</i> with the same 'font-size', 
+      compute an ideal position averaged from its font metrics.
+      To prevent superscripts and subscripts from throwing this position off-kilter,
+      an inline with a non-initial computed 'vertical-align'
+      is treated as having the ideal underline position of its parent.
       Position the portion of the line across each decorated fragment at that position.
+
+      <p class='issue'>
+        For simplicity, line-throughs should draw over each element at that element's preferred/averaged position.
+        This can produce some undesirable jumpiness,
+        but there doesn't appear to be any way to avoid that which is correct in all instances,
+        and all attempts are worryingly complex.
+        What position should line-throughts adopt over elements that have a different font-size,
+        but no <i>considered text</i>?
   </dl>
 
   <p>