Fanis
Personally I find "Attach a file" pretty clear, but it could be
ambiguous for the first time user who may think a folder could also be
attached but can't select one in the file browser that pops up. How
would you remove the ambiguity?
Fanis
As to how to remove the ambiguity? I don't think it's possible; the
word "file" meaning a single item is too firmly entrenched in the
culture of computing. Eventually there will be no more adult
first-timers to be confused about it.
For now, I usually just explain it ... as many times as it takes. I
just regret it when I don't get the chance to explain. (I distribute
customized music files to our local chorus, and there are all too many
folks who won't go near an attachment. Navigation boxes are too
scary!)