Why are there in
biblatex (e.g. using authortitle-comp in the bibliography) no concatenated roles when Person X is only annotator and the author of the introduction? In other words, I get often
Author, Book title. With annotations by John Doe. With an introduction by John Doe. Oxford: 2001.
Why is it not possible to have
Author, Book title. With an introduction and annotations by John Doe. Oxford: 2001.
Such concatenated roles are not defined in the documentation of
biblatex (http://ftp.uni-erlangen.de/ctan/macros/latex/contrib/biblatex/doc/biblatex.pdf -- see esp. "184.108.40.206 Concatenated Editor Roles, Expressed as Functions").