docs: function setSkipStageStep(that, stageId, stepId, value, method) {
          if ('string' !== typeof stageId || stageId.trim() === '') {
              throw new TypeError('Stager.' + method + ': stageId must ' +
                                  'be a non-empty string. Found: ' + stageId);
          }
          if (stepId) {
              if ('string' !== typeof stepId || stepId.trim() === '') {
                  throw new TypeError('Stager.' + method + ': stepId must ' +
                                      'be a non-empty string or undefined.' +
                                      'Found: ' + stepId);
              }
              if ('undefined' !== typeof value) {
                  that.toSkip.steps[stageId + '.' + stepId] = value;
              }
              return that.toSkip.steps[stageId + '.' + stepId];
          }
          if ('undefined' !== typeof value) that.toSkip.stages[stageId] = value;
          return that.toSkip.stages[stageId];
      }