--- a/microdata-rdf/index.html	Tue Oct 18 18:43:55 2011 -0700
+++ b/microdata-rdf/index.html	Wed Oct 26 12:37:16 2011 -0700
@@ -47,6 +47,7 @@
                     }
                     // now do terms
                     refs = document.querySelectorAll('tdef') ;
+                    var tdefs = [];
                     for (var i = 0; i < refs.length; i++) {
                         var item = refs[i];
                         if (!item) continue ;
@@ -57,10 +58,15 @@
                             ref = item.textContent ;
                         }
                         if (ref) {
-                            ref = ref.replace(/\n/g, '_') ;
-                            ref = ref.replace(/\s+/g, '_') ;
+                            ref = ref.replace(/\s+/g, '_').toLowerCase() ;
                         }
+
+                        if ( tdefs[ref]) {
+                          throw "Duplicate definition of term '" + ref + "'" ;
+                        }
+
                         var sp = document.createElement( 'dfn' ) ;
+                        tdefs[ref] = sp ;
                         sp.title = ref ;
                         sp.innerHTML = con ;
                         p.replaceChild(sp, item) ;
@@ -77,10 +83,12 @@
                             ref = item.textContent ;
                         }
                         if (ref) {
-                            ref = ref.replace(/\n/g, '_') ;
-                            ref = ref.replace(/\s+/g, '_') ;
+                            ref = ref.replace(/\s+/g, '_').toLowerCase() ;
                         }
 
+                        if ( !tdefs[ref]) {
+                          throw "Reference to undefined term '" + ref + "'" ;
+                        }
                         var sp = document.createElement( 'a' ) ;
                         var id = item.textContent ;
                         sp.className = 'tref' ;
@@ -369,7 +377,7 @@
           to ensure that values returned are consisted with this spec.
         </div>
         <dl>
-          <dt>If the element also has an <tref>itemscope</tref> attribute</dt>
+          <dt>If the element also has an <aref>itemscope</aref> attribute</dt>
           <dd>
             The value is the <tref>item</tref> created by the element as a <tref>URI reference</tref> or
             <tref>blank node</tref>
@@ -572,7 +580,7 @@
                 following the last SOLIDUS U+002F ("/") or NUMBER SIGN U+0023 ("#") in <em>type</em> and append
                 the fragment escaped value of <em>name</em>. If <em>type</em> contains no
                 SOLIDUS U+002F ("/") or NUMBER SIGN U+0023 ("#") it may not be used for generating a predicate
-                URI; skip this property and any associated <tref>property value</tref>s
+                URI; skip this property and any associated <tref>property value</tref>s.
               </li>
               <li>
                 Let <em>value</em> be the <tref>property value</tref> of <em>element</em>.