docs: function isolateCoverGrammar(parser) {
          var oldIsBindingElement = isBindingElement,
              oldIsAssignmentTarget = isAssignmentTarget,
              oldFirstCoverInitializedNameError = firstCoverInitializedNameError,
              result;
          isBindingElement = true;
          isAssignmentTarget = true;
          firstCoverInitializedNameError = null;
          result = parser();
          if (firstCoverInitializedNameError !== null) {
              throwUnexpectedToken(firstCoverInitializedNameError);
          }
          isBindingElement = oldIsBindingElement;
          isAssignmentTarget = oldIsAssignmentTarget;
          firstCoverInitializedNameError = oldFirstCoverInitializedNameError;
          return result;
      }