from mount(1): > A mountpoint can surely accept multiple binds/mounts with "-c", can't it?
-c This can be used in addition to any of the above to permit creation in a union directory. When a new file is created in a union directory, it is placed in the first element of the union that has been bound or mounted with the -c flag. If that directory does not have write permission, the cre- ate fails. you can do it, but it doesn't make any sense. only the last element added will be placed first in the union and thus writable at the root. - erik