gtk:tooltip-set-custom (tooltip widget)

tooltip -- a gtk:tooltip object
widget -- a gtk:widget custom widget, or nil to unset the old custom widget

Replaces the widget packed into the tooltip with widget. The widget argument does not get destroyed when tooltip goes away. By default a box with a gtk:image widget and gtk:label widget is embedded in the tooltip, which can be configured using the gtk:tooltip-set-markup and gtk:tooltip-set-icon functions.