Bug#812119: devscripts: uscan; Files-Excluded syntax is not specified anywhere

[Wookey]

Package: devscripts
Version: 2.15.3
Severity: normal

The uscan Files-Excluded field than can be put into debian/copyright
is a very nice feature, however it is currently unecessarily difficult
to use because it's format is not actually documented anywhere I could
find.

uscan refers to the existence of the Files-Excluded field in
debian/copyright in the man page, but does not give any details of its
format.

uscan --verbose helpfully reports if it does not understand the
specified copyright file:
WARNING: The file debian/copyright mentions Files-Excluded, but its
format is not recognized. Specify Format:
https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/ in
order to remove files from the tarball with mk-origtargz.

However
https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
does not contain the text 'Files-Excluded' anywhere in it.

By experimentation I have determined that: 

Files-Excluded is a 'Whitespace-spearated list' field, and it must be
in the Header Paragraph or it will be ignored. There can only be one
instance of the field in the 'Header' paragraph otherwise the above
error will be generated. 'Files' paragraphs can contain a
Files-Excluded field without error, but it will be ignored. The syntax
and wildcard matching is the same as the 'Files:' field.

This information should be documented, at least in the uscan manpage
and/or the mk-origtargz manpage.
The field should at least be mentioned in the doc at
https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/ and
referred to as something processed by uscan/mk-origtargz.

(It would be nice if more than one Files-Excluded field was allowed,
and that they would be concatenated, then each entry can be commented with
the reason for the exclusion, but I guess that is a separate wishlist
bug)