In the documentation for .gitattributes, "[[:space:]]" is mentioned in a code snippet but is not documented, and neither is the glob syntax escape from the documentation page for .gitignore ("\ ") not working with .gitattributes.
For example, in a .gitattributes file the first glob will work, but the second will not.
my[[:space:]]directory/**/* my\ directory/**/*
The opposite is true with .gitignore.
I got caught up for a number of minutes trying to figure out why my escapes weren't working in the fancy-pants .gitattributes I whipped up, and I'd figured it'd be worth saving someone else the trouble. It could very well be documented somewhere I'm not aware of beside the code snippet, but I wasn't able to find it seldom a github issues search, so I think it'd be worth putting on the .gitattributes page.
PS -- Apologies for not having a diff to send to fix this, but I don't currently have the tools available to me.