ATX,Micro ATX, Flex ATX,full ATX, could someone explain the differences..

[XRdirtHead]

I'm trying to build an inexpensive computer for my daughter for her room. I found a cheap case on newegg and it states
Motherboard Compatibility: ATX up to 12''x13''
could someone let me know about compatibility with the new ATX form factors. I was hoping to put a micro ATX mobo in this case and what is Flex ATX
Thanks
Ed

 

[eplebnista]

FormFactors.org

 

[XRdirtHead]

cool...thanks