Clarify how validation builds off of core.

This addresses issue #346, where it was not clear whether all
aspects of the core spec were relevant to validation.

Author: handrews

jsonschema-validation.xml

@@ -84,8 +84,8 @@
                 is also defined to assist in interactive user interface instance generation.
             </t>
             <t>
-                This specification will use the terminology defined by the
-                <xref target="json-schema">JSON Schema core</xref> specification.
+                This specification will use the concepts, syntax, and terminology defined
+                by the <xref target="json-schema">JSON Schema core</xref> specification.
             </t>
         </section>