/usr/share/lilypond/2.18.2/scm/document-identifiers.scm is in lilypond-data 2.18.2-4.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 | ;;;; This file is part of LilyPond, the GNU music typesetter.
;;;;
;;;; Copyright (C) 2006--2012 Han-Wen Nienhuys <hanwen@lilypond.org>
;;;;
;;;; LilyPond is free software: you can redistribute it and/or modify
;;;; it under the terms of the GNU General Public License as published by
;;;; the Free Software Foundation, either version 3 of the License, or
;;;; (at your option) any later version.
;;;;
;;;; LilyPond is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;;; GNU General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU General Public License
;;;; along with LilyPond.  If not, see <http://www.gnu.org/licenses/>.
(use-modules (ice-9 format))
(define (document-music-function music-func-pair)
  (let*
      ((name-sym (car music-func-pair))
       (music-func (cdr music-func-pair))
       (func (ly:music-function-extract music-func))
       (arg-names
        (map symbol->string
             (cddr (cadr (procedure-source func)))))
       (doc (procedure-documentation func))
       (sign (ly:music-function-signature music-func))
       (type-names (map (lambda (pred)
                          (if (pair? pred)
                              (format #f "[~a]" (type-name (car pred)))
                              (format #f "(~a)" (type-name pred))))
                        sign))
       (signature-str
        (string-join
         (map (lambda (arg type) (format #f "@var{~a} ~a" arg type))
              arg-names (cdr type-names)))))
    (format #f
            "@item @code{~a} ~a ~a~a
@funindex ~a
~a
"
            name-sym (car type-names)
            (if (string-null? signature-str) "" " - ") signature-str
            name-sym
            (if doc
                doc
                (begin
                  (ly:warning "music function `~a' not documented." name-sym)
                  "(undocumented; fixme)")))))
(define (document-object obj-pair)
  (and (ly:music-function? (cdr obj-pair))
       (document-music-function obj-pair)))
(define-public (identifiers-doc-string)
  (format #f
          "@table @asis
~a
@end table
"
          (string-join
           (filter-map
            document-object
            (sort
             (ly:module->alist (current-module))
             identifier<?)))
          ""))
 |