pandoc/citeproc issues: multiple bibliographies, nocite, citeonly

[John MacFarlane <fiddlosopher-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Currently pandoc inserts the list of works cited at the end
of the document.  (You can provide a label like

    # References

at the end if you like; the references will be placed after
this.)

This doesn't offer much flexibility. In particular:

(1)  The writer doesn't know which part is a bibliography and
can't style it differently or even offer the option to do so through
CSS, etc.  (Unlike the footnotes...)

(2)  You can't choose not to include the works cited.

(3)  You can't have per-section bibliographies in your document;
the bibliography only comes at the very end, even if you've got
a long book.

(4) There's currently no way to include items you didn't cite,
or suppress items you did cite.

There's a proposal at

    http://gitit.net/PandocCitationGrammar

that would address (2-4) by requiring the user to put an explicit

    <references />

tag where the bibliography goes; this would then turn into a list of
works cited since the last <references />.  It would include attributes
to "omit" or "include" citation keys.  (I suppose we could even have
a "source" tag that specifies the bib file to use, but this would
only work if we no longer had to read the bib file prior to parsing
the markdown -- see the previous "issue".)

We could address (1) as well by adding a special Bibliography block
to pandoc.  This would have some cost, as each writer would have to
be told how to treat it, but it would give more flexibility. For
example, in HTML, the bibliography could be put in a special
<div>. (Note that with the current system, if you want your bibliography in a
div, you can put it in a section and use the --section-divs option.)

I'd like to get some feedback on whether we want this flexibility,
or whether the current simple behavior sufficies.

John