code: function(key, enabled) {
        var val = enabled;
        if (key === undefined) {
          return this;
        }
        if (val === undefined) {
          val = this.map[key] === undefined;
        }
        return this.value(key, val === true ? true : null);
      }
docs: Set or toggle the enabled status of a given key.
  
  <p>If the <em>enabled</em> parameter is not passed, then the enabled
  status will be toggled to its opposite value.</p>
  
  @param {String} key they key to set
  @param {Boolean} enabled the optional enabled value to set
  @returns {sn.Configuration} this object to allow method chaining
  @preserve