[css-text] Styling of soft hyphens

Closes #3863

Author: frivoal

css-text-3/Overview.bs

@@ -2739,6 +2739,22 @@ Line Breaking Details</h3>
       or the HTTP <code>Content-Language</code> header)
       in order to obtain correct automatic hyphenation.
 
+      The character or characters visually shown due to hyphenation
+      at a [=hyphenation opportunity=] created by a conditional hyphen character (&amp;shy; or U+00AD)
+      are inserted in-place,
+      and styled according to any property that applies to the conditional hyphen character.
+
+      <div class=example>
+        <pre><code highlight=html>ex&lt;span style="color:red">&amp;shy;&lt;/span>ample</code></pre>
+
+        <p>When the markup above is hyphenated, it is rendered as
+        <span style="display: inline-block; background: white; border: solid 1px; vertical-align: middle; padding: 0 1ch;">
+          ex<span style="color:red;">-</span><br>
+          ample
+        </span>
+      </div>
+
+
     <p>When shaping scripts such as Arabic are allowed to break within words
       due to hyphenation,
       the characters must still be shaped