addOperatorDecorator (decoratorOrName, cb) {
    this.operators.addOperatorDecorator(decoratorOrName, cb)
  }
Add a custom operator decorator
@param {string}   decoratorOrName - decorator identifier within the condition; i.e. instead of 'someFact', 'everyValue', etc
@param {function(factValue, jsonValue, next)} callback - the method to execute when the decorator is encountered.