List items are now identified by an attribute, defined by the
idAttribute option. By default the id
attribute is used.
The serialization format has changed to
{expanded: [id...], collapsed: [id...], version: 2}. The
previous format returned by serialize() is also
supported.
Unnecessary entries are excluded from serialization data structure
(items without ids or children need not be included).
Checkbox ids are now sequential - if you want to address a checkbox
use a selector that targets “.the-list-item > input”.
Remove the need for guid, generatedIdPrefix, specifiedIdPrefix and
adding generated ids to list items.