[css-writing-modes] More clarifications, more in line with <https://lists.w3.org/Archives/Public/www-style/2015Aug/0290.html>

Author: fantasai

css-writing-modes/Overview.bs

@@ -930,19 +930,6 @@ Obsolete SVG1.1 'writing-mode' Values</h4>
     specification. The additional ''tb-lr'' value of that revision is
     replaced by ''vertical-lr''.
 
-  <p>UAs that only need to support the SVG presentational attribute syntax,
-    but not the CSS syntax, for these values
-    may instead use UA style sheet rules to make the mapping:
-
-  <pre highlight=css>
-    @namespace svg "http://www.w3.org/2000/svg";
-    svg|*[writing-mode=lr], svg|*[writing-mode=lr-tb],
-    svg|*[writing-mode=rl], svg|*[writing-mode=rl-tb] {
-      writing-mode: horizontal-tbl; }
-    svg|*[writing-mode=tb], svg|*[writing-mode=tb-rl] {
-      writing-mode: vertical-rl; }
-  </pre>
-
   <div class="note">
     In SVG1.1, these values set the <dfn>inline progression direction</dfn>,
     in other words, the direction the current text position
@@ -957,6 +944,27 @@ Obsolete SVG1.1 'writing-mode' Values</h4>
     text string or reverse the order of all glyphs in the text.
   </div>
 
+  <p>In order to support legacy content,
+  and to allow authors to create documents that support older clients,
+  SVG UAs must add the following style sheet rules to their default UA stylesheet:
+
+  <pre highlight=css>
+    @namespace svg "http://www.w3.org/2000/svg";
+    svg|*[writing-mode=lr], svg|*[writing-mode=lr-tb],
+    svg|*[writing-mode=rl], svg|*[writing-mode=rl-tb] {
+      writing-mode: horizontal-tbl; }
+    svg|*[writing-mode=tb], svg|*[writing-mode=tb-rl] {
+      writing-mode: vertical-rl; }
+  </pre>
+
+  <div class="note">
+    Authors who wish to create forwards and backwards-compatible content
+    in CSS syntax can use the CSS forwards-compatible parsing rules to do so,
+    e.g.
+    
+    <pre>svg|text { writing-mode: tb; writing-mode: vertical-rl; }</pre>
+  </div>
+
 <h2 id="inline-alignment">
 Inline-level Alignment</h2>