def set_pkg_file_name(self, doc, name):
self.assert_package_exists()<EOL>if not self.package_file_name_set:<EOL><INDENT>self.package_file_name_set = True<EOL>doc.package.file_name = name<EOL>return True<EOL><DEDENT>else:<EOL><INDENT>raise CardinalityError('<STR_LIT>')<EOL><DEDENT>
Sets the package file name, if not already set.
        name - Any string.
        Raises CardinalityError if already has a file_name.
        Raises OrderError if no pacakge previously defined.