find-file-name-handler

find-file-name-handler is a built-in function in `C source code'.

(find-file-name-handler FILENAME OPERATION)

Return FILENAME's handler function for OPERATION, if it has one.
Otherwise, return nil.
A file name is handled if one of the regular expressions in
`file-name-handler-alist' matches it.

If OPERATION equals `inhibit-file-name-operation', then we ignore
any handlers that are members of `inhibit-file-name-handlers',
but we still do run any other handlers. This lets handlers
use the standard functions without calling themselves recursively.