code: function _setEventHandler(type, handler) {
      if (!this._handlers) this._handlers = Object.create(null);
      this._handlers[type] = handler;
    }
docs: An event handler is like an event listener, but it registered by setting an IDL or content attribute like onload or onclick. There can only be one of these at a time for any event type. This is an internal method for the attribute accessors and content attribute handlers that need to register events handlers. The type argument is the same as in addEventListener(). The handler argument is the same as listeners in addEventListener: it can be a function or an object. Pass null to remove any existing handler.  Handlers are always invoked before any listeners of the same type.  They are not invoked during the capturing phase of event dispatch.