Generalize $schema from "version" to "feature set"

Author: handrews

jsonschema-core.xml

@@ -803,9 +803,9 @@
         <section title="Meta-Schemas and Vocabularies">
             <section title='The "$schema" Keyword'>
                 <t>
-                    The "$schema" keyword is both used as a JSON Schema version identifier and the
-                    location of a resource which is itself a JSON Schema, which describes any schema
-                    written for this particular version.
+                    The "$schema" keyword is both used as a JSON Schema feature set identifier and
+                    the location of a resource which is itself a JSON Schema, which describes any
+                    schema written for this particular feature set.
                 </t>
                 <t>
                     The value of this keyword MUST be a <xref target="RFC3986">URI</xref>