Labels for each bibliography entry within an entry set with biblatex

Question

I have a few references that consist of several bibliography entries that are grouped via biblatex's command \defbibentryset (using biber as backend). The standard behaviour of biblatex is to seperate the entries by a semicolon without any further labelling. I wonder wether there is a possibility to assign a label (arabic or roman numbers or letters) to each of the entries so that it looks like

[1] a) bibliography entry; b) bibliograhpy entry; c) ...

Answer 1

Sometimes the entrysetcount field really comes in handy. :-)

\documentclass{article}

\usepackage[backend=biber]{biblatex}

\DeclareFieldFormat{bibentrysetcount}{\mknumalph{#1})\addhighpenspace}
\renewbibmacro*{begentry}{%
  \printfield[bibentrysetcount]{entrysetcount}%
}

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@misc{A01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
}
@misc{B02,
  author = {Buthor, B.},
  year = {2002},
  title = {Bravo},
}
@misc{C03,
  author = {Cuthor, C.},
  year = {2003},
  title = {Charlie},
}
\end{filecontents}

\addbibresource{\jobname.bib}

\nocite{A01}

\defbibentryset{set}{B02,C03}

\begin{document}

\printbibliography

\end{document}

EDIT: \addhighpenspace discourages line breaks after the label, but does not forbid them. As for the format of entrysetcount: I should have used the bibentrysetcount format -- example corrected.

EDIT 2: Another advantage of using the bibentrysetcount format is that one can drop the \iffieldundef test -- example corrected again.