callback
The command procedure to be executed when the mouse moves while a button is pressed within the contents area of a window during menu polling. The window identifier is passed to the procedure as a parameter.
If neither this procedure nor the window’s .down nor .up procedures have been defined, the window’s .exec procedure is executed on receipt of a mouse press. Additionally if the window’s .exec procedure has an associated pulldown menu (tied to the window.exec_button element) then that .exec procedure is executed in preference to the .down, .drag or .up procedures.
Within this procedure, any command or function which normally requires an interactive mouse action from the user will return with the current mouse position without requiring the operator to use the mouse.
New windows have a .drag procedure of null.
window.drag (<window>)