resolves #1019 - added language to explicitly specify behavior when a vocab is known

Author: gregsdennis

jsonschema-core.xml

@@ -1198,7 +1198,9 @@
                         vocabularies available for use in schemas described by that meta-schema.
                         It is also used to indicate whether each vocabulary is required or optional,
                         in the sense that an implementation MUST understand the required vocabularies
-                        in order to successfully process the schema.
+                        in order to successfully process the schema.  Any vocabulary that is
+                        understood by the implementation MUST be processed in a manner consistent
+                        with the semantic definitions contained within the vocabulary.
                     </t>
                     <t>
                         The value of this keyword MUST be an object.  The property names in the
@@ -1226,7 +1228,8 @@
                         the vocabulary MUST refuse to process any schemas that declare
                         this meta-schema with "$schema".  If the value is false, implementations
                         that do not recognize the vocabulary SHOULD proceed with processing
-                        such schemas.
+                        such schemas.  The value has no impact if the implementation
+                        recognizes the vocabulary.
                     </t>
                     <t>
                         Per <xref target="extending" format="counter"></xref>, unrecognized