New functions

Implent function ->cache()

If you create the function 'cache' and have it return cache parameters then caching for your box will be taken care of.
Example return value would be:

       array( 
        'cache' => BLOCK_CACHE_CONTENT_CACHE,
        'cache_keys' => array(
          'node' => array('node_type' => 'node_type'),
          'os_og' => array('current' => 'current'),
        ));  

Where 'cache' defines the type of caching to use, currently 'BLOCK_CACHE_CONTENT_CACHE' is the only option.
'cache_keys' defines when the cache for this block should be cleared. In the example above the cache will be cleared any time a node of type 'node_tpye' is saved within the current site. For more information on avalible keys see the "Views content cache" module.

Implent function ->access()

Control when a widget is avalible to an administrator of a site, for example return false if a required feature for this block is not avalible.

Plugin Definition

"title"

A Title must be present for your plugin to be included in the list of avalible boxes

Standard Vsite Widget keys

Additionally your plugin definition can add any key provided in the vsite widgets hook.

"module dependencies"

You may provide an array of modules that should be enabled. This can include features and the box will be disabled if the feature is not enabled in the site.