Where to put sgml file

I have a package that will have an sgml file.  One of the demos in ./demo
will use it.  Where should I put it?

I tried putting it in ./demo but it did not survive the build so
currently I put it in ./inst and it gets copied to the same level as the
DESCRIPTION file and the demo gets it from there.  Is that right or
is there a better choice?  I assume I can't use ./data since its not in
the form that is directly readable as an R data file.