In my bachelor thesis I have a few references that consist of several bibliography entries that are grouped via biblatex's command \defbibentryset (using biber as backend). Now I wonder if it is possible to add some text within these grouped entries, for example to indicate an erratum paper by adding something like "(E)" after the entry:

[1] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996, 77, 3865; J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1997, 78, 1396 (E).

Another example would be the creation of a reference with grouped entries that should look like this:

[2] E. H. Lieb, „Density Functionals for Coulomb Systems“ in Physics as Natural Philosophy: Essays in Honor of Laszlo Tisza on His 75th Birthday (Eds.: A. Shimony, H. Feshbach), MIT Press, Cambridge, MA, 1982, pp. 111–149; a revised version appeared in E. H. Lieb, Int. J. Quantum Chem. 1983, 24, 243.

In the last example the phrase "a revised version appeared in" is the part that should be added to biblatex's standard output.
My question is: Can this be achieved with biblatex (or another package) or do I have to make these changes manually in the *.bbl file.

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Just a note for completeness - the general issue with related entries like "a revised version appeared in" etc. will be addressed by biblatex probably around the Autumn this year. We already have very decent general functionality for this in biber and are working on the biblatex interface. – PLK Jul 31 '11 at 17:20
@PLK: Thanks for the info. It would have surprised me if no one else would have stumbled across this issue. I'm looking forward to see what this functionality will look like in biblatex. – Philipp Jul 31 '11 at 18:11
According to the biblatex developer, it's one of the most requested extensions, things like "reprinted as", or "included in" fields etc. So it was necessary to come up with a general way of dealing with such things without just adding a load of fields arbitrarily. The solution is a couple of generic fields which cause biber to auto-create some "data only" entries. This is rather nice and works because biber instantiates data source entries in an internal biblatex data model well before any bbl output. – PLK Jul 31 '11 at 20:10

In your first example, "(E)" may simply be added by using the addendum field of the corresponding bibentry. For your second example, I suggest to also use the addendum field (in this case the one of the "Lieb 1982" bibentry) and to remove the closing semicolon by adding \nopunct at the end of the addendum field.

\documentclass{article}

\usepackage{biblatex}

\renewbibmacro{in:}{%
\ifentrytype{article}{}{%
\printtext{\bibstring{in}\intitlepunct}}}

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@incollection{Lie82,
author = {Lieb, E. H.},
year = {1982},
title = {Density Functionals for Coulomb Systems},
booktitle = {Physics as Natural Philosophy: Essays in Honor of Laszlo Tisza on His 75th Birthday},
editor = {Shimony, A., and Feshbach, H.},
location = {Cambridge, \mkbibacro{MA}},
publisher = {\mkbibacro{MIT} Press},
pages = {111--149},
addendum = {A revised version appeared in\nopunct},
}
@article{Lie83,
author = {Lieb, E. H.},
year = {1983},
journaltitle = {Int. J. Quantum Chem.},
volume = {24},
pages = {243},
}
\end{filecontents}


 Thank you very much. This produces the output I desired. Of course, I would prefer not to meddle too much with the *.bib files but as PLK pointed out in his comment there will be some functionality added in biblatex to solve the problem and so your solution will help me format my thesis the way I intended. But I have a little question concerning your answer: Why do you use smallcaps (via the \mkbibacro command) for MIT and MA? Is this a common thing in bibliographies? – Philipp Jul 31 '11 at 17:58 @Philipp: I think small caps do look nicer because they don't stand as much out. For two- or three-letter abbrevations it's a matter of taste; longer acronyms like UNESCO cry for small caps. – lockstep Jul 31 '11 at 18:10 Ah, you definetly have a point there. I thought it might also be some kind of typographical rule, which would have been an interesting information for me in view of the documents I have to write in the future. – Philipp Jul 31 '11 at 18:28