I'm using autocomplete and I want to my webserver to return an additionnal field for each entry in the array, "tooltip", which I would use to create a tooltip for each choice when doing mouseover over them.
Right now, open event doesn't pass anything in the UI parameter, but it has access to the content array (which the response event receive). If the content array was passed to "open", then that event could do the required modification before opening the menu by iterating over each element in the "ui" parameter and all the <li>.
An alternative would be to have an "updated" event which would be called after the choices are rendered and would receive the content array too.