[css-text-3] Ignore inline element boundaries for hyphenation

See w3c#3862

Author: frivoal

css-text-3/Overview.bs

@@ -2723,6 +2723,11 @@ Line Breaking Details</h3>
         hyphens/hyphens-auto-001.html
       </wpt>
 
+      <p>For the purpose of the 'hyphens' property,
+      what constitutes a “word” is UA-dependent.
+      However, inline element boundaries
+      must be ignored when determining word boundaries.
+
     <p class="advisement">
       Authors should correctly tag their content’s <a lt="content language">language</a>
       (e.g. using the HTML <code>lang</code> attribute