code: function (id, value, options, doNotSave) {
              return this.base.set(this.prefix + id, value, options, doNotSave);
          }
docs: Sets the prefixed preference
  
  @param {string} id Identifier of the preference to set
  @param {Object} value New value for the preference
  @param {{location: ?Object, context: ?Object}=} options Specific location in which to set the value or the context to use when setting the value
  @param {boolean=} doNotSave True if the preference change should not be saved automatically.
  @return {valid:  {boolean}, true if no validator specified or if value is valid
  stored: {boolean}} true if a value was stored