code: function setOpt(oldProp, oldType, target, rename) {
          const types = utils.ensureArray(oldType);
          if (oldProp in opts && types.indexOf(typeOf(opts[oldProp])) >= 0) {
              target[rename || oldProp] = opts[oldProp];
          }
      }
docs: HELPER HELPERS :P 
  Sets the given option to the new-structure options if it's set in
  the old/provided. If doesn't exist, it's already set on the new via
  defaults.
  @private
  
  @param {String} oldProp - Property/option name to be checked on the
  old-structure options.
  @param {String|Array} oldType - Expected type(s) of `prop` on the
  old-structure options.
  @param {Object} target - Target object of the new-structure template
  options which the value will be set on.
  @param {String} [rename] - New property/option name to be set on the
  new-structure options.