DEVELOPER NEEDED
I'm sorry to say that I am not able to keep the pace developing this project anymore. I know how much nestedSortable is important for web applications, and I still can't understand why it's not part of jQuery-UI. I also think the base of the plugin is very strong, and deserves much more attention and involvement. If anybody is willing to take this project, please say so here.
Thank you.

nestedSortable jQuery plugin

nestedSortable is a jQuery plugin that extends jQuery Sortable UI functionalities to nested lists.
Note: Version 2.0 is published in branch '2.0alpha' and is ready for testing! At the moment it has only been tested in Firefox and Chrome, if you work with IE feel free to give it a shot and let me know if something goes wrong.

Features

Designed to work seamlessly with the nested set model (have a look at the toArray method)
Items can be sorted in their own list, moved across the tree, or nested under other items.
Sublists are created and deleted on the fly
All jQuery Sortable options, events and methods are available
It is possible to define elements that will not accept a new nested item/list and a maximum depth for nested items
The root level can be protected

Usage

<ol class="sortable">
	<li><div>Some content</div></li>
	<li>
		<div>Some content</div>
		<ol>
			<li><div>Some sub-item content</div></li>
			<li><div>Some sub-item content</div></li>
		</ol>
	</li>
	<li><div>Some content</div></li>
</ol>

	$(document).ready(function(){

		$('.sortable').nestedSortable({
			handle: 'div',
			items: 'li',
			toleranceElement: '> div'
		});

	});

Please note: every <li> must have either one or two direct children, the first one being a container element (such as <div> in the above example), and the (optional) second one being the nested list. The container element has to be set as the 'toleranceElement' in the options, and this, or one of its children, as the 'handle'.

Also, the default list type is <ol>.

Custom Options

tabSize: How far right or left (in pixels) the item has to travel in order to be nested or to be sent outside its current list. Default: 20
disableNesting: The class name of the items that will not accept nested lists. Default: ui-nestedSortable-no-nesting
errorClass: The class given to the placeholder in case of error. Default: ui-nestedSortable-error
listType: The list type used (ordered or unordered). Default: ol
maxLevels: The maximum depth of nested items the list can accept. If set to '0' the levels are unlimited. Default: 0
protectRoot: Wether to protect the root level (i.e. root items can be sorted but not nested, sub-items cannot become root items). Default: false
rootID: The id given to the root element (set this to whatever suits your data structure). Default: null
rtl: Set this to true if you have a right-to-left page. Default: false
isAllowed (function): You can specify a custom function to verify if a drop location is allowed. Default: function(item, parent) { return true; }

Custom Methods

serialize

Serializes the nested list into a string like setName[item1Id]=parentId&setName[item2Id]=parentId, reading from each item's id formatted as 'setName_itemId' (where itemId is a number). It accepts the same options as the original Sortable method (key, attribute and expression).

toArray

Builds an array where each element is in the form:

setName[n] =>
{
	'item_id': itemId,
	'parent_id': parentId,
	'depth': depth,
	'left': left,
	'right': right,
}

It accepts the same options as the original Sortable method (attribute and expression) plus the custom startDepthCount, that sets the starting depth number (default is 0).

toHierarchy

Builds a hierarchical object in the form:

'0' ...
	'id' => itemId
'1' ...
	'id' => itemId
	'children' ...
		'0' ...
			'id' => itemId
		'1' ...
			'id' => itemId
'2' ...
	'id' => itemId

Similarly to toArray, it accepts attribute and expression options.

Known Bugs

nestedSortable doesn't work properly with connected draggables, because of the way Draggable simulates Sortable mouseStart and mouseStop events. This bug might or might not be fixed some time in the future (it's not specific to this plugin).

Requirements

jQuery 1.4+
jQuery UI Sortable 1.8+

Browser Compatibility

Tested with: IE 6/7/8, Firefox 3.6/4, Chrome, Safari 3

License

This work is licensed under the MIT License.

This work is pizzaware. If it saved your life, or you just feel good at heart, please consider offering me a pizza. This can be done in two ways: (1) follow this link to donate through paypal; (2) send me cash via traditional mail to my home address in Italy. Is the second method legal? It is in Italy if you use Posta assicurata. You should check with your local laws if you live elsewhere.

dragonfire1119 / nestedSortable