bibtex-autokey-abbrev is a compiled Lisp function in `bibtex.el'.

(bibtex-autokey-abbrev STRING LEN)

Return an abbreviation of STRING with at least LEN characters.
If LEN is positive the abbreviation is terminated only after a consonant
or at the word end. If LEN is negative the abbreviation is strictly
enforced using abs (LEN) characters. If LEN is not a number, STRING
is returned unchanged.