bibtex-field-braces-alist syntax

Question

I'm struggling with using bibtex-field-braces-alist to format titles in Bibtex entries. I've set this as

(setq bibtex-field-braces-alist
      '((("title") . ("N2O" "European"))))

My interpretation of the variable's documentation (below) is that this should cause bibtex-clean-entry to change the title field "Western European N2O emissions" to "Western {European} {N2O} emissions". However, nothing happens for me :( I have added "braces" to bibtex-entry-format:

(setq bibtex-entry-format '(opts-or-alts required-fields numerical-fields braces)) 

bibtex-field-braces-alist’s value is ((("TITLE") "N2O" "European")) Original value was nil

You can customize this variable.

Documentation: Alist of field regexps that C-c C-c encloses by braces. Each element has the form (FIELDS REGEXP), where FIELDS is a list of BibTeX field names and REGEXP is a regexp. Space characters in REGEXP will be replaced by "[ \t\n]+".

Answer 1

Try

(setq bibtex-field-braces-alist
      '((("title") "N2O\\|European")))

Rationale: a REGEXP is represented by a string, not a list. Here you want a regexp that will match the string "N2O" or the string "European". That is done with the alternation construct \| (see Regexps Backslash in the Emacs manual). Note that backslashes have to be doubled in strings that are to be read by the Lisp reader - see this SE Emacs question for more details on this wrinkle.

Just tested it and it seems to work.

EDIT: In response to your comment about restarting emacs to get the change to take effect, that is one way to do it. The problem is that there is another variable, bibtex-field-braces-opt, that is set from bibtex-field-braces-alist after some munging, but only if that variable is nil. So to get the change to take effect without restarting emacs, you also have to change that variable:

(setq bibtex-field-braces-opt nil)

One good way to avoid such problems would be to use Customize to change bibtex-field-braces-alist, which should be set up to reset the other variable when you change this one by calling bibtex-field-re-init, but AFAICT it is not: that should probably be reported as a bug. Ditto for bibtex-field-strings-alist and bibtex-field-strings-opt.