Some files are neither directories nor regular files: they are unusual
files like symbolic links, device special files, named pipes, and
sockets. Currently, diff treats symbolic links like regular files;
it treats other special files like regular files if they are specified
at the top level, but simply reports their presence when comparing
directories. This means that patch cannot represent changes
to such files. For example, if you change which file a symbolic link
points to, diff outputs the difference between the two files,
instead of the change to the symbolic link.
diff should optionally report changes to special files specially,
and patch should be extended to understand these extensions.