function checkComplex( actual, expected ) {
	var entries;
	var match;
	var type;

	match = RE_INSTANCE_ANNOTATION.exec( expected );
	if ( match ) {
		type = match[ 1 ];
		entries = match[ 2 ];
		if ( actual.constructor.name !== type ) {
			return 'Expected instance type <'+type+'>, but observed <'+actual.constructor.name+'>';
		}
		if ( entries ) {
			if ( isComplex128( actual ) ) {
				actual = [ real( actual ), imag( actual ) ];
			} else if ( isComplex64( actual ) ) {
				actual = [ realf( actual ), imagf( actual ) ];
			}
			return compareEntries( actual, parse( entries ) );
		}
		return null;
	}
	return 'Complex numbers should be documented using instance annotation';
}
Checks whether a complex number matches the expected return annotation.

@private
@param {*} actual - actual return value
@param {string} expected - return value annotation
@returns {(string|null)} error message or null