8.1 Breaking a localname into its components

TRAMP file names are somewhat different, obviously, to ordinary file names. As such, the lisp functions file-name-directory and file-name-nondirectory are overridden within the TRAMP package.

Their replacements are reasonably simplistic in their approach. They dissect the file name, call the original handler on the localname and then rebuild the TRAMP file name with the result.

This allows the platform specific hacks in the original handlers to take effect while preserving the TRAMP file name information.