Biber ignores the characters of junk it complains about, so technically you can consider that still a comment. Biber will (contrary to BibTeX), however, ignore everything after a %
without a warning.
So if you start a line (outside an entry) with %
, that line is considered a comment by both BibTeX and Biber.
The BibTeX example file xampl.bib
(described as "a database file with an example of every standard entry type") starts with
% Copyright (C) 1988, 2010 Oren Patashnik.
so that seems to be an "officially sanctioned" way to add a comment in .bib
files.
%
; it will also ignore the characters of junk it complains about. See also Are comments discouraged in a BibTeX file?