A gadget is a graphical element which responds to user input. Gadgets are implemented as tuples which (directly or indirectly) inherit from gadget, which in turn inherits from rect.

gadget

Gadgets are arranged in a hierarchy, and all visible gadgets except for instances of world are contained in a parent gadget, stored in the parent slot.
Gadget geometry
Gadget hierarchy and layouts
Pre-made UI gadgets
Top-level windows
Status bars and mouse-over help

See also
Models