add 'annotation collection only' requirement

Author: gregsdennis

jsonschema-core.xml

@@ -629,6 +629,10 @@
                         The values of keywords which begin with the "@" symbol MUST be
                         collected as annotations.
                     </t>
+                    <t>
+                        Keywords which begin with the "@" symbol MUST NOT affect evaluation
+                        of a schema in any way other than annotation collection.
+                    </t>
                     <t>
                         Consequently, the "@" symbol is reserved for this purpose, and
                         extension vocabularies which define keywords that start with "@"