Downgrade splitting grapheme clusters to a warning.

Author: fantasai

css3-text/Overview.html

@@ -467,8 +467,9 @@ <h3 id=terms><span class=secno>1.3. </span> Terminology</h3>
   <p>The rendering characteristics of a <a
    href="#character"><i>character</i></a> divided by an element boundary is
    undefined: it may be rendered as belonging to either side of the boundary,
-   or as some approximation of belonging to both. Authors should avoid
-   dividing grapheme clusters by element boundaries.
+   or as some approximation of belonging to both. Authors are forewarned that
+   dividing grapheme clusters by element boundaries may give inconsistent
+   results.
 
   <h2 id=transforming><span class=secno>2. </span> Transforming Text</h2>
 

css3-text/Overview.src.html

@@ -189,8 +189,8 @@ <h3 id="terms">
   <p>The rendering characteristics of a <i>character</i> divided by an
     element boundary is undefined: it may be rendered as belonging to
     either side of the boundary, or as some approximation of belonging
-    to both. Authors should avoid dividing grapheme clusters by element
-    boundaries.
+    to both. Authors are forewarned that dividing grapheme clusters by
+    element boundaries may give inconsistent results.
 
 <h2 id="transforming">
   Transforming Text</h2>