gtk::paint_focus() is a convenience function that draws a dark shadow along the left and top sides of the given rectangle, making it appear as GTK widgets generally do when they have focus.

This is the only function that uses the detail parameter at all now; if you pass 'set-mode' as that parameter, the shadow will appear as long dashes rather than as a continuous line. Any other string is regarded the same as if it were null.

The other parameters are on the whole self-explanatory. The widget parameter refers to the widget that is being drawn upon (usually a GtkDrawingArea).