--- a/html-data-guide/index.html	Wed Dec 21 16:43:38 2011 +0000
+++ b/html-data-guide/index.html	Wed Dec 21 20:42:43 2011 +0000
@@ -184,6 +184,9 @@
         <p>
           All three <a title="syntax">syntaxes</a> follow a similar data model. Each is used to describe <dfn title="entity">entities</dfn> &mdash; things such as people or events (RDFa calls these resources, microdata calls these items). These entities each have one or more <dfn title="type">types</dfn> which indicate what kind of thing they are and a number of <dfn title="property">properties</dfn> that have <dfn title="value">values</dfn>, which provide the data about the entity. The main difference is that in the RDF generated from RDFa, the entities are arranged in a graph, whereas the default data model for microformats and microdata is a tree.
         </p>
+        <p>
+          <a title="type">Types</a>, <a title="property">properties</a> and <a title="entity">entities</a> can be identified in different ways. Microformats uses short names. RDFa, like RDF, uses <a href="http://tools.ietf.org/html/rfc3987" class="externalDFN">IRIs</a>, while microdata uses <a href="http://dev.w3.org/html5/spec/urls.html#url" class="externalDFN">URLs</a> as defined in HTML5. This document tries to use the appropriate term (IRI or URL) when discussing identifiers, but sometimes uses the term URL to mean a URL or IRI. See also <a href="#iris" class="sectionRef"></a> for more detail around the use of identifiers in microdata and RDFa.
+        </p>
       </section>
       
     </section>