How gtk+ get the default font of system?

["yandong.yao" <Yandong Yao Sun COM>]

Hi guys,

   I use gnome-font-properties to configure my default application font 
to "Arial Regualr 13", and then i write one pure gtk+ application which 
just show one label in the gtk window, and this gtk+  application will 
use 'Arial Regular 13' to display, I am wondering why my configuration 
through gconf can take effect on pure gtk+ applications immediately(need 
not restart), there is no any gconf function call in gtk+ code.  could 
anybody give me some hints on this?

Regards,
Yandong