How to change command line auto-completion rules

[Rashkae]

Rashkae wrote:
> I would like to use Xine to play flv files.  That's easy enough to
> associate with the  GUI, but how can I configure the command line
> Auto-complete so .flv files are seen as a valid option to pass to xine?
>  I don't think I need step by step, but I have no idea where to even
> begin looking for these rules.
> 

I don't know what possessed me to spam the list before trying even a
basic Google search.  Sorry everyone.

For future posterity, the answer I was looking for was /etc/bash_completion.