can-delete? in text%
Called before a range is deleted from the editor.
If the return value is #f, then the
delete will be aborted.
The editor is internally locked for writing during a call to this method
(see also Locks). Use
after-delete to modify the editor, if necessary.
See also
on-delete,
after-delete, and
on-edit-sequence.
( -> boolean
send a-text can-delete? start len)
start : exact non-negative integer
len : exact non-negative integer
The start argument specifies the starting position of the range
to delete. The len argument specifies number of items to
delete (so start + length is the ending position of the
range to delete).