what is variation file?

Hi, guys,

Can anyone tell me what a variation file is? e.g. I read the document crc compiler user guide, inside which it says:

A generator variation file, crcgen.v(hd) for a single channel MegaCore function or crcgen_multichan.v(hd) for a multichannel MegaCore function.

why does it end with .v? isn't that for verilog file? Why do they call it a different name as variation file?

Thanks a lot!