




The type of arguments for the callbacks.
The callback for selecting an item.
The callback for extending the selection.
callbacks-callback-type
callbacks-selection-callback
callbacks-extend-callback
callbacks-retract-callback
callbacks-action-callback
Each callback function can be one of the following:
Call the function.
Apply the head of the list to the tail.
Call redisplay-interface on the top-level interface.
Call redisplay-menu-bar on the top-level interface.
The slot value callback-type determines which arguments get passed to each of the callbacks. It can be any of the following values, and passes the corresponding data to the callback function:
(
item-data
)
(
item
)
(
interface
)
(
item-data
 
item
 
interface
)
The pane with the current input focus.
()
()
callback-type
 can also be a list containing any of 
:focus
, 
:data
, 
:interface
, 
:collection
, 
:item
.
The 
item-data
 variable is the item's data if the item is of type item, otherwise it is the item itself, as for 
item. 
The 
item
 variable means the item itself. The 
interface
 is the 
element-interface
 of the element. 
collection
 is the element's collection, if there is one.