[css-writing-modes] Add some notes clarifying that used 'direction' is influenced by text-orientation and writing-mode.

Author: fantasai

css-writing-modes-3/Overview.bs

@@ -1223,6 +1223,7 @@ Orienting Text: the 'text-orientation' property</h3>
       are typeset with their intrinsic orientation.
       See <a href="#vertical-orientations">Vertical Orientations</a> for further details.
     <p>This value is typical for layout of dominantly vertical-script text.
+
     <dt><dfn>upright</dfn></dt>
     <dd><p>In vertical writing modes,
       <a>typographic character units</a> from horizontal-only scripts
@@ -1231,9 +1232,17 @@ Orienting Text: the 'text-orientation' property</h3>
       <a>Typographic character units</a> from vertical scripts
       are typeset with their intrinsic orientation and shaped normally.
       See <a href="#vertical-orientations">Vertical Orientations</a> for further details.
-      <p>This value causes the used value of 'direction' to be ''ltr'',
+      <p>This value causes the <a>used value</a> of 'direction' to be ''ltr'',
       and for the purposes of bidi reordering,
       causes all characters to be treated as strong LTR.
+
+      Note: The <a>used value</a>, rather than the <a>computed value</a>,
+      of 'direction' is influenced
+      so that ''rtl'' can inherit properly
+      into any descendants
+      (such as the contents of a <a lt="horizontal writing mode">horizontal</a> inline-block)
+      where this directional override does not apply.
+
     <dt><dfn>sideways</dfn></dt>
     <dd><p>In vertical writing modes,
       this causes all text to be <a href="#typeset-sideways">typeset sideways</a>,
@@ -1764,6 +1773,12 @@ Abstract-to-Physical Mappings</h3>
     </tbody>
   </table>
 
+  Note: The <a lt="used value">used</a> 'direction'
+  depends on the computed 'writing-mode' and 'text-orientation':
+  in <a>vertical writing modes</a>,
+  a 'text-orientation' value of ''text-orientation/upright''
+  forces the used 'direction' to ''ltr''.
+
 <h2 id="abstract-layout">
 Abstract Box Layout</h2>
 

css-writing-modes-4/Overview.bs

@@ -1300,6 +1300,7 @@ Orienting Text: the 'text-orientation' property</h3>
       are typeset with their intrinsic orientation.
       See <a href="#vertical-orientations">Vertical Orientations</a> for further details.
     <p>This value is typical for layout of dominantly vertical-script text.
+
     <dt><dfn>upright</dfn></dt>
     <dd><p>In vertical writing modes,
       <a>typographic character units</a> from horizontal-only scripts
@@ -1308,9 +1309,17 @@ Orienting Text: the 'text-orientation' property</h3>
       <a>Typographic character units</a> from vertical scripts
       are typeset with their intrinsic orientation and shaped normally.
       See <a href="#vertical-orientations">Vertical Orientations</a> for further details.
-      <p>This value causes the used value of 'direction' to be ''ltr'',
+      <p>This value causes the <a>used value</a> of 'direction' to be ''ltr'',
       and for the purposes of bidi reordering,
       causes all characters to be treated as strong LTR.
+
+      Note: The <a>used value</a>, rather than the <a>computed value</a>,
+      of 'direction' is influenced
+      so that ''rtl'' can inherit properly
+      into any descendants
+      (such as the contents of a <a lt="horizontal writing mode">horizontal</a> inline-block)
+      where this directional override does not apply.
+
     <dt><dfn>sideways</dfn></dt>
     <dd><p>In vertical writing modes,
       this causes all text to be <a href="#typeset-sideways">typeset sideways</a>,
@@ -1860,6 +1869,12 @@ Abstract-to-Physical Mappings</h3>
     </tbody>
   </table>
 
+  Note: The <a lt="used value">used</a> 'direction'
+  depends on the computed 'writing-mode' and 'text-orientation':
+  in <a>vertical writing modes</a>,
+  a 'text-orientation' value of ''text-orientation/upright''
+  forces the used 'direction' to ''ltr''.
+
 <h2 id="abstract-layout">
 Abstract Box Layout</h2>