x-dnd-default-test-function

x-dnd-default-test-function is a compiled Lisp function in `x-dnd.el'.

(x-dnd-default-test-function WINDOW ACTION TYPES)

The default test function for drag and drop.
WINDOW is where the mouse is when this function is called. It may be
a frame if the mouse is over the menu bar, scroll bar or tool bar.
ACTION is the suggested action from the source, and TYPES are the
types the drop data can have. This function only accepts drops with
types in `x-dnd-known-types'. It always returns the action private.