code: function is( instance, Class ) {
  		switch ( typeof Class ) {
  			case 'function' : return instance instanceof Class;
  			case 'string'   : return ( Class = get( Class ) ) ? ( instance instanceof Class ) : false;
  		}
  		return false;
  	}
docs: function get_return_value( ctx, value ) { return ctx[__chain__] === true && value === UNDEF ? ctx : value; }