known_hosts file format

[Theo Markettos]

Is there something that defines the .ssh/known_hosts file format anywhere?  
I'm writing an ssh client for another platform (where OpenSSH doesn't port
very well), and I'd like to keep the known_hosts file the same format so
it is interchangeable with other clients.  Is hostfile.c the only
documentation around.  Is this format likely to be stable?

Thanks,
Theo