Coding Quake3Radiant? Unreal Editor?... GL..

Hullo everyone!
I am Gautam From india!
Well just a fresh veg. entering into the world of open gl !

Ok, can someone tell me that Editors like q3radiant, and unrea editor etc are all coded using opengl api?

I mean does coding all these require very much HITECH understanding of pure win 32 programming? Do guide me! Just briefly!

Till Then,
Frag For Fun!