Improve note.

Author: gkellogg

index.html

@@ -1620,7 +1620,8 @@ <h3>Algorithm</h3>
           to <code>false</code>.</li>
         <li class="changed">If <var>value</var> contains the <a>entry</a> <code>@id</code> and its value
           neither equals <var>term</var> nor is <code>null</code>:
-          <div id="ctd-id-null" class="note">If `null`, the term is not used for IRI expansion, but is
+          <div id="ctd-id-null" class="note">If the `@id` entry is `null`,
+            the term is not used for IRI expansion, but is
             retained to be able to detect future redefinitions of this term.</div>
           <ol>
             <li>If the value associated with the <code>@id</code> <a>entry</a> is not a <a>string</a>, an