[css-text-3] Improve cross-linking.

Author: fantasai

css-text-3/Overview.bs

@@ -4751,8 +4751,9 @@ Word Spacing: the 'word-spacing' property</h3>
           word-spacing-characters-001.xht
       </wpt>
 
-      If there are no word-separator characters, or if a word-separating
-      character has a zero advance width (such as the zero width space U+200B)
+      If there are no [=word-separator characters=],
+      or if a [=word-separating character=] has a zero advance width
+      (such as the zero width space U+200B)
       then the user agent must not create an additional spacing between words.
 
       <wpt pathprefix="css/CSS2/text">
@@ -4761,7 +4762,7 @@ Word Spacing: the 'word-spacing' property</h3>
 
       General punctuation
       and fixed-width spaces (such as U+3000 and U+2000 through U+200A)
-      are not considered word-separator characters.</p>
+      are not considered [=word-separator characters=].
 
       <wpt pathprefix="css/CSS2/text">
           word-spacing-characters-002.xht