I believe this was a typo but I have to say that I was not able to get it to work in this form (I ended up using the same construct as in the rust example: %global _description \).

I believe the original is right. I have been doing it this way for some time:

%global foo %{expand:
foo
bar
}

This was not a typo.

hm, ok then may I suggest we put the } in a new line as @decathorpe presented? I put some enphasis to it and helps seeing it (I had not seen it until now).

I don't mind either way.

If you put the closing } onto a new line, the variable will contain a trailing newline. If you don't, it won't. Do whatever is appropriate for where you will use that value :)

BTW: Do you have a snippet where this doesn't work as expected? Without that, it's hard to tell what's going wrong.