Add notion of transparency in 1.5 Triple Terms and Reification

Author: franconi

spec/index.html

@@ -324,6 +324,9 @@ <h3>Triple Terms and Reification</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>RDF terms that appear in a triple term have the same denotation as when they appear in an asserted triple in the graph. 
+      For this reason, we say that triple terms are <i>transparent</i>.</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>;
       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>.