gtk:tooltip-set-custom (tooltip widget)

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

Replaces the widget packed into the tooltip with a custom widget. widget does not get destroyed when the tooltip goes away. By default a box with a gtk:image 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.