Re: gitattributes don't work

Marcin Wiśnicki [off-list ref] writes:

I'm trying to exclude certain paths (those that contain "xmac/gen/") from 
diff output using .git/info/attributes (not .gitattributes).

According to gitattributes(5) it supports patterns from gitignore(5).

Example path that must be excluded:
src/byucc/jhdl/CSRC/xmac/gen/and2_dp_g.xmac

What I've tried but didn't work:
xmac/gen/ -diff

Why not "xmac/gen/* -diff" or even "xmac/gen/*.xmac -diff"?