clarify the requirements to implement the different output formats

Author: karenetheridge

jsonschema-core.xml

@@ -2644,9 +2644,9 @@
                             structure that matches the exact structure of the schema.
                         </t>
                     </list>
-                    An implementation SHOULD provide at least the "flag", "basic", or "detailed"
-                    format and MAY provide the "verbose" format.  If it provides one or more of the
-                    complex formats, it MUST also provide the "flag" format. Implementations SHOULD
+                    An implementation SHOULD provide at least one the "flag", "basic", or "detailed"
+                    format and MAY provide the "verbose" format.  If it provides one or more of the "detailed" or "verbose"
+                    formats, it MUST also provide the "flag" format. Implementations SHOULD
                     specify in their documentation which formats they support.
                 </t>