How should cvs-fast-export be properly ignorant?

I just shipped version 1.10 of cvs-fast-export with a new feature: it now emits fast-import files that contain CVS’s default ignore patterns. This is a request for help from people who know CVS better than I do.

I’ve written before about the difference between literal and literary repository translations. When I write translation tools, one of my goals is for the experience of using the converted repository to as though the target system had been in use all along. Notably, if the target system has changesets, a dumb file-oriented conversion from CVS just isn’t good enough.

Another goal is for the transition to be seamless; that is, without actually looking for it, a developer browsing the history should not need to be aware of when the transition happened. This implies that the ignore patterns of the old repository should be emulated in the new one – no object files (for example) suddenly appearing under git status when they were invisible under CVS.

There is one subtle point I’m not sure of, though. and I would appreciate correction from anyone who knows CVS well enough to say. If you specify a .cvsignore, does it add to the default ignore patterns or replace them?

My current assumption in 1.10 is that it adds to them. If someone corrects me on this, I’ll remove a small anount of code and ship 1.11.