improve working around namespace table

Author: pchampin

spec/index.html

@@ -271,10 +271,11 @@ <h3>RDF Vocabularies and Namespace IRIs</h3>
     <p>The <a>IRIs</a> in an <a>RDF vocabulary</a> often begin with
       a common substring known as a <dfn>namespace IRI</dfn>.
       Some namespace IRIs are associated by convention with a short name
-      known as a <dfn>namespace prefix</dfn>. Some examples:
+      known as a <dfn>namespace prefix</dfn>.
+      The table below provides some examples.
 
     <table id="tab-vocab-ns" class="simple">
-      <caption>Some example namespace prefixes and IRIs</caption>
+      <caption>Some namespace prefixes and IRIs used in this specification</caption>
       <tr>
         <th>Namespace prefix</th>
         <th>Namespace IRI</th>