code: function register(element, handlerName, options) {
      var handler = HANDLERS[handlerName.replace(/^\$md./, '')];
      if (!handler) {
        throw new Error('Failed to register element with handler ' + handlerName + '. ' +
        'Available handlers: ' + Object.keys(HANDLERS).join(', '));
      }
      return handler.registerElement(element, options);
    }
docs: Register an element to listen for a handler.
  This allows an element to override the default options for a handler.
  Additionally, some handlers like drag and hold only dispatch events if
  the domEvent happens inside an element that's registered to listen for these events.
  
  @see GestureHandler for how overriding of default options works.
  @example $mdGesture.register(myElement, 'drag', { minDistance: 20, horizontal: false })