Unspecified pieces

The TDS cannot address the following aspects of a functioning TeX system:

1. The location of executable programs: this is too site-dependent even to recommend a location, let alone require one. A site may place executables outside the `texmf' tree altogether (e.g., `/usr/local/bin'), in a platform-dependent directory within `texmf', or elsewhere.
2. Upgrading packages when new releases are made: we could find no way of introducing version specifiers into `texmf' that would do more good than harm, or that would be practical for even a plurality of installations.
3. The location of implementation-specific files (e.g., TeX `.fmt' files): by their nature, these must be left to the implementor or TeX maintainer. See Section section Example implementation-specific trees.
4. Precisely when a package or file should be considered "local", and where such local files are installed. See Section section Local additions for more discussion.

• Portable filenames

Portable filenames

The TDS cannot require any particular restriction on filenames in the tree, since the names of many existing TeX files conform to no standard scheme. For the benefit of people who wish to make a portable TeX distribution or installation, however, we outline here the necessary restrictions. The TDS specifications themselves are compatible with these.

ISO-9660 is the only universally acceptable file system format for CD-ROMs. A subset thereof meets the stringent limitations of all operating systems in use today. It specifies the following:

• File and directory names, not including any directory path or extension part, may not exceed eight characters.
• Filenames may have a single extension. Extensions may not exceed three characters. Directory names may not have an extension.
• Names and extensions may consist of only the characters `A'--`Z', `0'--`9', and underscore. Lowercase letters are excluded.
• A period separates the filename from the extension and is always present, even if the name or extension is missing (e.g., `FILENAME.' or `.EXT').
• A version number, ranging from 1--32767, is appended to the file extension, separated by a semicolon (e.g., `FILENAME.EXT;1').
• Only eight directory levels are allowed, including the top-level (mounted) directory (see Section section Rooting the tree). Thus, the deepest valid ISO-9660 path is:

  texmf/L2/L3/L4/L5/L6/L7/L8/FOO.BAR;1
  1     2  3  4  5  6  7  8
  

  The deepest TDS path needs only seven levels:

  texmf/fonts/pk/cx/public/cm/dpi300/cmr10.pk
  1     2     3  4  5      6  7
  

Some systems display a modified format of ISO-9660 names, mapping alphabetic characters to lowercase, removing version numbers and trailing periods, etc.

Before the December 1996 release, LaTeX used mixed-case names for font descriptor files. Fortunately, it never relied on case alone to distinguish among the files. Nowadays, it uses only monocase names.