can-insert?

Called before a snip is inserted from the editor. If the return value is #f, then the insert will be aborted.

See also on-insert and after-insert.

The editor is internally locked for writing when this method is called (see also Locks).

• (send a-pasteboard can-insert? snip before x y) -> boolean
      snip : snip% object
      before : snip% object or #f
      x : real number
      y : real number