def set_doc_comment(self, doc, comment):
if not self.doc_comment_set:<EOL><INDENT>self.doc_comment_set = True<EOL>doc.comment = comment<EOL><DEDENT>else:<EOL><INDENT>raise CardinalityError('<STR_LIT>')<EOL><DEDENT>
Sets document comment, Raises CardinalityError if
        comment already set.