file-name-handler-alist

file-name-handler-alist is a variable defined in `C source code'.
Its value is

(("\\(?:\\.dz\\|\\.txz\\|\\.xz\\|\\.lzma\\|\\.lz\\|\\.g?z\\|\\.\\(?:tgz\\|svgz\\|sifz\\)\\|\\.tbz2?\\|\\.bz2\\|\\.Z\\)\\(?:~\\|\\.~[-[:alnum:]:#@^._]+\\(?:~[[:digit:]]+\\)?~\\)?\\'" . jka-compr-handler)
 ("\\.gpg\\(~\\|\\.~[0-9]+~\\)?\\'" . epa-file-handler)
 ("\\`/[^/]*\\'" . tramp-completion-file-name-handler)
 ("\\`/[^/|:][^/|]*:" . tramp-file-name-handler)
 ("\\`/:" . file-name-non-special))

• This variable may be risky if used as a file-local variable.

Documentation:
Alist of elements (REGEXP . HANDLER) for file names handled specially.
If a file name matches REGEXP, all I/O on that file is done by calling
HANDLER. If a file name matches more than one handler, the handler
whose match starts last in the file name gets precedence. The
function `find-file-name-handler' checks this list for a handler for
its argument.

HANDLER should be a function. The first argument given to it is the
name of the I/O primitive to be handled; the remaining arguments are
the arguments that were passed to that primitive. For example, if you
do (file-exists-p FILENAME) and FILENAME is handled by HANDLER, then
HANDLER is called like this:

(funcall HANDLER 'file-exists-p FILENAME)

Note that HANDLER must be able to handle all I/O primitives; if it has
nothing special to do for a primitive, it should reinvoke the
primitive to handle the operation "the usual way".
See Info node `(elisp)Magic File Names' for more details.