reftex-convert-string
    
    reftex-convert-string is a compiled Lisp function in `reftex.el'.
(reftex-convert-string STRING SPLIT-RE INVALID-RE DOT KEEP-FP NWORDS MAXCHAR INVALID ABBREV SEP IGNORE-WORDS &optional DOWNCASE)
Convert a string (a sentence) to something shorter.
SPLIT-RE     is the regular expression used to split the string into words.
INVALID-RE   matches characters which are invalid in the final string.
DOT          t means add dots to abbreviated words.
KEEP-FP      t means to keep a final punctuation when applicable.
NWORDS       Number of words to use.
MAXCHAR      Maximum number of characters in the final string.
INVALID      nil: Throw away any words containing stuff matched with INVALID-RE.
             t:   Throw away only the matched part, not the whole word.
ABBREV       nil: Never abbreviate words.
             t:   Always abbreviate words (see `reftex-abbrev-parameters').
             not t and not nil: Abbreviate words if necessary to shorten
                                string below MAXCHAR.
SEP          String separating different words in the output string.
IGNORE-WORDS List of words which should be removed from the string.