Added comment about the effects on well-formedness checking after

calling XML_UseForeignDTD(parser, XML_TRUE).

expat/lib/expat.h

@@ -679,6 +679,9 @@ XML_UseParserAsHandlerArg(XML_Parser parser);
    specified in the document. In such a case the parser will call the
    externalEntityRefHandler with a value of NULL for the systemId
    argument (the publicId and context arguments will be NULL as well).
+   Note: For the purpose of checking WFC: Entity Declared, passing
+     useDTD == XML_TRUE will make the parser behave as if the document
+     had a DTD with an external subset.
    Note: If this function is called, then this must be done before
      the first call to XML_Parse or XML_ParseBuffer, since it will
      have no effect after that.  Returns