* Axel Beckert <abe@debian.org>, 2014-08-24, 11:39:
$ apt-cache policy foobar W: Unknown Multi-Arch type 'no' for package 'libcdio-dev' W: Unknown Multi-Arch type 'no' for package 'libiso9660-dev' W: Unknown Multi-Arch type 'no' for package 'libudf-dev'
According to deb-control(5), "no" is a valid value for the Multi-Arch field. (Although it's the default, so it would be probably better to omit the field.)
-- Jakub Wilk