def set_doc_comment(self, doc, comment):
if not self.doc_comment_set:<EOL><INDENT>self.doc_comment_set = True<EOL>if validations.validate_doc_comment(comment):<EOL><INDENT>doc.comment = str_from_text(comment)<EOL>return True<EOL><DEDENT>else:<EOL><INDENT>raise SPDXValueError('<STR_LIT>')<EOL><DEDENT><DEDENT>else:<EOL><INDENT>raise CardinalityError('<STR_LIT>')<EOL><DEDENT>
Sets document comment, Raises CardinalityError if
        comment already set.
        Raises SPDXValueError if comment is not free form text.