comment / uncomment region

[exits funnel]

Hello,

I'm having trouble getting comment-region and
uncomment-region to work in the .grammar files I'm
editing.  I'm pretty new to Emacs but I understnad
they don't work because there is no major mode for
these sablecc grammar files.  I've looked at the doc a
bit and I understand that I have to set the variable
comment-start to "//" but when I evaluate (setq
comment-start) in the scratch buffer it seems to
change the value only for that buffer.  Can anyone
give me a jump start here?  Ideally, I'd like to be
able to put something in my .emacs file which will set
its value for any active .grammar file, but I'd be
satisfied if I could at least figure out how to set it
interactively for the current buffer.  Thanks in
advance.

-exits

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