can-insert? (augmentable only) in text%

Called before items are inserted into the editor. If the return value is #f, then the insert will be aborted.

The editor is internally locked for writing during a call to this method (see also Locks). Use after-insert to modify the editor, if necessary.

See also on-insert, after-insert, and on-edit-sequence.

• (send a-text can-insert? start len) -> boolean
     start : exact non-negative integer
     len : exact non-negative integer

  The start argument specifies the position of the potential insert. The len argument specifies the total length (in positions) of the items to be inserted.