def get_heading_types(self):
<EOL>from .osid_errors import IllegalState<EOL>if self._kwargs['<STR_LIT>'] not in ['<STR_LIT>']:<EOL><INDENT>raise IllegalState()<EOL><DEDENT>else:<EOL><INDENT>return self._kwargs['<STR_LIT>']<EOL><DEDENT>
Gets the set of acceptable heading types.

        return: (osid.type.Type) - a set of heading types or an empty
                array if not restricted
        raise:  IllegalState - syntax is not a ``HEADING``
        *compliance: mandatory -- This method must be implemented.*