Core: Clarify about infinite loops

Author: awwright

jsonschema-core.xml

@@ -306,7 +306,7 @@
                 operation when they encounter a network-addressible URI.
             </t>
             <t>
-                A schema MUST NOT be run against an instance more than once. For example, if two schemas "#alice" and "#bob"
+                A schema MUST NOT be run into an infinite loop against a schema. For example, if two schemas "#alice" and "#bob"
                 both have an "allOf" property that refers to the other, a naive validator might get stuck in an infinite recursive
                 loop trying to validate the instance.
             </t>