Add allow-end value to punctuation trim.

Author: fantasai

css3-text/Overview.src.html

@@ -1835,7 +1835,7 @@ <h3 id="punctuation-trim"><span class="secno">7.3.</span>
         </tr>
         <tr>
           <th>Value:</th>
-          <td>none | [start || end || adjacent]
+          <td>none | [start || [ end | allow-end ] || adjacent]
           </td>
         </tr>
         <tr>
@@ -1880,6 +1880,10 @@ <h3 id="punctuation-trim"><span class="secno">7.3.</span>
       <dt><dfn title="punctuation-trim:end">end</dfn></dt>
       <dd>Trim (kern) the blank half of fullwidth closing punctuation at
         the end of each line.</dd>
+      <dt><dfn title="punctuation-trim:allow-end">allow-end</dfn></dt>
+      <dd>Trim (kern) the blank half of fullwidth closing punctuation at
+        the end of each line if it does not otherwise fit prior to
+        justification.</dd>
       <dt><dfn title="punctuation-trim:adjacent">adjacent</dfn></dt>
       <dd>Trim (kern) the blank half of fullwidth opening punctuation if its
         previous adjacent character is a fullwidth opening punctuation,