Using ${description}, and debian/substvars.

[Shaul Karl <shaulk@actcom.net.il>]

  Quoting http://bugs.debian.org/209569

    If this package is being generated from a single source package and
    you already provide a full description in your control file for the
    main package, you might want to use it automatically in
    sub-packages. If this is the case consider using ${description},
    and debian/substvars.
 
Can you tell where using ${description} and debian/substvars being
documented, and give some examples for package which are made from a
single source package and automate using the description in 
sub-packages?
-- 

    Shaul Karl,    shaulk @ actcom . net . il