These are biblatex-specific multicite commands that allow for multiple
pre- and postnotes, as in:
\cites(pre)(post)[pre1][post1]{key1}[pre2][post2]{key2}...
with an optional general pre- and postnote, which applies to the whole
list (like [][] in normal cite commands) and an optional pre- and
postnotes for each item, so that pagination can actually be specified in
multi-cite references, as in:
(cf. Miller 2015, 2; furthermore Smith 2013, 23-23; Jenkins 2012, 103,
also refer to chapter 6 in this book)
See the biblatex manual, sec. 3.8.3., for details.
File format change.