Update 2006-12-08: My "Generator Guide" has now become a part of the official Firebird Documentation Project, which can be found here:

http://www.firebirdsql.org/index.php?op=devel&sub=doc

The guide has been updated and revised by Paul Vinkenoog (thanks Paul!). It now also includes documentation on the new Sequence syntax that is available in Firebird 2.

The document is available online as html or as PDF for download. There is also a german and a russian translation available. Just follow the link above!