I just found out by looking at the source code that currently the files base_include and base_exclude are not documented. udeb_include and udeb_exclude ARE documented, e.g. in d-i-cvs/doc/retriever.txt -- Try Linux 2.6 from BitKeeper for PXA2x0 CPUs at http://www.mn-logistik.de/unsupported/linux-2.6/