code: function(field, binning) {
              if (!this.dataModelObject.hasField(field)) {
                  throw new Error("Did not find field " + field);
              }
              var f = this.dataModelObject.fieldByName(field);
              if ("timestamp" !== f.type) {
                  throw new Error("Field was of type " + f.type + ", expected timestamp.");
              }
              if (!utils.contains(this._binning, binning)) {
                  throw new Error("Invalid binning " + binning + " found. Valid values are: " + this._binning.join(", "));
              }
  
              this.columns.push({
                  fieldName: field,
                  owner: f.owner,
                  type: f.type,
                  period: binning
              });
  
              return this;            
          }
docs: Add a column split on a timestamp valued field, binned by the specified bucket size.
  
  @param {String} fieldName The name of field to split on.
  @param {String} binning The size of bins to use, see class docs for valid types.
  @return {splunkjs.Service.PivotSpecification} The updated pivot specification.
  
  @method splunkjs.Service.PivotSpecification