Having accepted the necessity for subdirectory searching, the TWG turned its attention next to other constraints placed on the TDS. The other constraints arise because it must be possible to use the TDS on any platform.
Many, but not all, operating systems disregard the distinction between upper- and lowercase letters in filenames. The ISO-9660 format (described below) does not allow mixed-case names. The TDS does not require monocase names, although it is clear that mixed-case filenames may cause problems in some environments. Filenames which are identical except with respect to case are particularly likely to be troublesome.
One use of the TDS will be the creation of mountable generic TeX-related distributions on CD-ROM. CD-ROM vendors will want to use ISO-9660 format because it is the only universally acceptable file system format for CD-ROMs. ISO-9660 is portable, but it imposes strict limitations on file and directory names:
texmf/L2/L3/L4/L5/L6/L7/L8/FOO.BAR;1 1 2 3 4 5 6 7 8
Here is the deepest TDS example, which needs only seven levels:
texmf/fonts/pk/cx/public/cm/dpi300/cmr10.pk 1 2 3 4 5 6 7
Note: Some systems display a modified format of ISO-9660 names, mapping alphabetic characters to lowercase, removing version numbers and trailing periods, etc. This does not affect the format of names on the CD-ROM itself.