code: function(handler, options) {
          var active = this.active;
          if(active) {
              this.deactivate();
          }
          this.handler = new handler(this, this.callbacks, options);
          if(active) {
              this.activate();
          }
      }
docs: Method: updateHandler
  
  Parameters:
  handler - {Function} One of the sketch handler constructors.
  options - {Object} Options for the handler.