"ui" parameter in jquery widget event handling

I'm trying to learn jquery and rummaging through jquery's documentation is not fun for a newbie.

I can't find any documentation on the "ui" parameter for sortables and their start() event handling function. The two params: event and ui. Where are the documentations that show detail of what the ui parameter does/has? What does ui.item show? ui.item.data?

The following link offers a little help but not enough detail.

What are event and UI parameters in Dialog

The link above states: "The ui parameter is typically a hash; its properties depend on the event being raised. For the dialog open event, both arguments appear to be null. For other events, such as dragStart, drag and dragStop, ui will contain the current position and offset"

So if the contents of ui parameter i开发者_StackOverflows dependent on the event being raised, where are the documentations that show this?

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Here is a page that I reference almost daily:

http://jqueryui.com/demos/

More specifically for sortable: http://jqueryui.com/demos/sortable/

The tabs below the examples explain all their is to know about the options, events and methods. The overview tab explains a little bit about what is in the ui and event objects that are passed back to the start event.

Also, here is a page that explains better what the jquery event object has and links to more info about the properties:

http://api.jquery.com/category/events/event-object/