src/perl/vms/vms.c:
/*
 *   Yet small as was their hunted band
 *   still fell and fearless was each hand,
 *   and strong deeds they wrought yet oft,
 *   and loved the woods, whose ways more soft
 *   them seemed than thralls of that black throne
 *   to live and languish in halls of stone.
 *        "The Lay of Leithian", Canto II, lines 135-40
 *
 *      [p.162 of _The Lays of Beleriand_]
 */

Every file in the perl src has that sort of comment at the top of it. It tells you what the file is there for. This is very important in code.

av.c:
/*
 * '...for the Entwives desired order, and plenty, and peace (by which they
 *  meant that things should remain where they had set them).' --Treebeard
 *
 *      [p.476 of _The Lord of the Rings_, III/iv: "Treebeard"]
 */
%%
deb.c:
/*
 * 'Didst thou think that the eyes of the White Tower were blind?  Nay,
 *  I have seen more than thou knowest, Grey Fool.'  --Denethor