How to ignore a token if it doesn't fit in with a rule?

[uclacasey]

I'm writing a program that handles comments as well as a few other things. If
a comment is in a specific place, then my program does something.

Flex passes a token upon finding a comment, and Bison then looks to see if
that token fits into a particular rule. If it does, then it takes an action
associated with that rule.

Here's the thing: the input I'm receiving might actually have comments in
the wrong places. In this case, I just want to ignore the comment rather
than flagging an error.

My question: 
How can I use a token if it fits into a rule, but ignore it if it doesn't?
Can I make a token "optional"?

(Note: The only way I can think of of doing this right now is scattering the
comment token in every possible place in every possible rule. There MUST be
a better solution than this. Maybe some rule involving the root?)
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