Tapespec
Lists of on-media parts are sometimes passed around in a "tapelist", implemented in common-src/tapelist.c. This is not to be confused with the tapelist file (which, naturally enough, is implemented in server-src/tapefile.c).
A tapelist is a semicolon-separated list of volumes, where each volume is specified as a label, a colon, and a comma-separated list of file numbers on that volume. For example:
Conf-001:1
or
Conf-001:3,4,5,9,11;Conf-002:1,2,3