Add an informative definition for "reifying triple". (#98)

* Add an informative definition for "reifying triple".

---------

Co-authored-by: Olaf Hartig <olaf.hartig@liu.se>
Co-authored-by: Ted Thibodeau Jr <tthibodeau@openlinksw.com>

spec/index.html

@@ -186,9 +186,11 @@ <h3>Triple Terms</h3>
       For a <a>triple term</a> to be asserted,
       it must also appear in a graph as an <a>asserted triple</a>.</p>
 
-    <p>A <a>triple term</a> can be used as the object of a <a>triple</a> with the predicate <code>rdf:reifies</code>.
+    <p>A <a>triple term</a> can be used as the object of a <a>triple</a> with the predicate <code>rdf:reifies</code>;
+      such a <a>triple</a> is then a <dfn>reifying triple</dfn>.
       The <a>subject</a> of that <a>triple</a> is called a <dfn>reifier</dfn>.
-      Assertions on the <a>triple term</a> are made using the <a>reifier</a>.</p>
+      Assertions on the <a>triple term</a> are made using the <a>reifier</a>.
+      A concrete syntax may provide a special notation for specifying <a>reifying triples</a>.</p>
 
     <p class="note">Using the <a>reifier</a> as an indirect way of referencing a <a>triple term</a>
       allows multiple groups of assertions to be separated from each other,
@@ -1826,7 +1828,8 @@ <h2>Changes between RDF 1.1 and RDF 1.2</h2>
    <li>Added <a href="#section-triple-terms" class="sectionRef"></a>
       and definitions for <a>triple term</a> and <a>asserted triple</a>
       and extended the definition of
-      <a>RDF triple</a> to permit triple terms as objects..
+      <a>RDF triple</a> to permit triple terms as objects.
+      Also defines <a>reifier</a> and <a>reifying triple</a>.</li>
     <li>Added the <a>base direction</a> element as part of 
       a <a>literal</a>,
       and a description of its use in <a href="#section-text-direction" class="sectionRef"></a>.</li>