what motherboard form factor does the power mac g5 use?

I have an old power mac g5 case which I'd like to re purpose into my new editing pc, and I am wondering if it uses a proprietary form factor motherboard, or a standard form factor motherboard like atx, micro atx, or mini itx to know if I'd have to do some case modding or not, thanks for all replies, and I know I will need to mod the cables within the case like the power button, so no need to make note of that! Also, I know it would take less effort just to get another case, but I'd like to work on this case.