gitignore patterns

Hi,

In the kernel tree, I see 2 .gitignore files that use "+pattern":

./arch/blackfin/include/asm/.gitignore:+mach
./arch/blackfin/boot/.gitignore:+vmImage

However, I can't find anything about '+' on the gitignore(5) man page
at http://www.kernel.org/pub/software/scm/git/docs/gitignore.html .

Does the '+' mean something special or is it just a character in the
filename/dir pattern?

Thanks,
-- 
~Randy