return value from expose event / draw signal of GtkDrawingArea

[Luca Bacci <luca bacci982 gmail com>]

Hi, does anyone know what meaning has the return value from expose event
handler (for gtk2) and draw signal (for gtk3) of GtkDrawingArea?

When one should return TRUE, and when FALSE?

I can't find any information in the reference manual

Thank you!
Luca