The vmdcallbacks and vmdmenu modules are only useful in the context of
GUI VMD using a compiled-in Python interpreter.
Callbacks are methods that are invoked whenever some GUI trigger happens,
for example, clicking an item in a menu. Adding callbacks is useful to
create interactive graphs or plugins that alter VMD or molecule state in
response to user input.
New menus can be added to the GUI using the vmdmenu module: