parse Markup declarations from an external subset  [30]
          extSubset ::= textDecl? extSubsetDecl  [31] extSubsetDecl
           ::= (markupdecl | conditionalSect | PEReference | S) *

def parseExternalSubset(self, ExternalID, SystemID):
        """parse Markup declarations from an external subset  [30]
          extSubset ::= textDecl? extSubsetDecl  [31] extSubsetDecl
           ::= (markupdecl | conditionalSect | PEReference | S) * """
        libxml2mod.xmlParseExternalSubset(self._o, ExternalID, SystemID)