[css-text-3] Editorial rewrite of bidi + line boxes section, for clarity. w3c#5759

Author: fantasai

css-text-3/Overview.bs

@@ -5667,22 +5667,40 @@ Cursive Scripts</h4>
 <h3 id="bidi-linebox">
 Bidirectionality and Line Boxes</h3>
 
-  <p>The <a spec=css-writing-modes-3>start</a> and <a spec=css-writing-modes-3>end</a> edges of a line box
+  <p>The <a spec=css-writing-modes-3>start</a> and <a spec=css-writing-modes-3>end</a> sides of a line box
     are determined by the <a>inline base direction</a> of the line box.
-    In most cases, this is given by its containing block's computed 'direction'.
-
-  <p>However if its containing block has ''unicode-bidi: plaintext'' [[!CSS-WRITING-MODES-3]],
-    the line box's <a>inline base direction</a> must be determined
-    by the <a>inline base direction</a> of the <a>bidi paragraph</a> to which it belongs:
-    that is, the <a>bidi paragraph</a> for which the line box holds content.
-    An empty line box
-    (i.e. one that contains no atomic inlines or
-     characters other than the line-breaking character, if any)
-    or one whose <a>bidi paragraph</a> has no strong directionality
-    (contains only weak or neutral characters),
-    takes its <a>inline base direction</a> from the preceding line box (if any), or,
-    if this is the first line box in the containing block,
-    then from the 'direction' property of the containing block.
+
+  <p class="note">Note: Although they usually match,
+    the [=inline base direction=] of a [=line box=]
+    is distinct from the [=inline base direction=] applied to its contents.
+    The [=line box=]’s [=inline base direction=] affects
+    'text-align-all', 'text-align-last', 'text-indent', and 'hanging-punctuation'--
+    i.e. the position and alignment of its contents with respect to its edges.
+    It does not affect the formatting or ordering of inline content,
+    which is controlled by the Unicode bidirectional algorithm
+    as applied by [[CSS-WRITING-MODES-3]].
+
+  <p>In most cases, a [=line box=]’s [=inline base direction=]
+  is given by its [=containing block=]'s computed 'direction'.
+  However if its [=containing block=] has ''unicode-bidi: plaintext'' [[!CSS-WRITING-MODES-3]]:
+
+  <ul>
+    <li>If the [=bidi paragraph=] to which the [=line box=] belongs
+      (that is, the <a>bidi paragraph</a> for which the line box holds content)
+      has strong directionality,
+      the line box's <a>inline base direction</a> is that direction.
+
+    <li>If the [=line box=] is empty
+      (i.e. contains no [=atomic inlines=] or
+      characters other than the newline character, if any)
+      or otherwise has no strong directionality
+      (contains only weak or neutral characters),
+      its <a>inline base direction</a> is taken
+      from the preceding line box (if any),
+      or, if this is the first line box in the containing block,
+      from the 'direction' property of the containing block.
+      (This can result in an RTL line box whose contents have an LTR base direction.)
+  </ul>
 
   <div class="example">
     <p>In the following example,
@@ -5701,11 +5719,6 @@ Bidirectionality and Line Boxes</h3>
       &lt;/block&gt;</pre>
   </div>
 
-  <p class="note">Note: The inline base direction determined here
-    applies to the line box itself, and not to its contents.
-    It affects 'text-align-all', 'text-align-last', 'text-indent', and 'hanging-punctuation',
-    i.e. the position and alignment of its contents with respect to its edges.
-    It does not affect the formatting or ordering of its content.
 
   <div class="example">
     <p>In the following example: