ff-search-directories

ff-search-directories is a variable defined in `find-file.el'.
Its value is

cc-search-directories

• Automatically becomes buffer-local when set.

Documentation:
List of directories to search for a specific file.

Set by default to `cc-search-directories', expanded at run-time.

This list is searched through with each extension specified in
`ff-other-file-alist' that matches this file's extension. So the
longer the list, the longer it'll take to realize that a file
may not exist.

A typical format is

'("." "/usr/include" "$PROJECT/*/include")

Environment variables can be inserted between slashes (`/').
They will be replaced by their definition. If a variable does
not exist, it is replaced (silently) with an empty string.

The stars are *not* wildcards: they are searched for together with
the preceding slash. The star represents all the subdirectories except
`..', and each of these subdirectories will be searched in turn.

You can customize this variable.