This protection is similar to protected_fifos, but it avoids writes to an attacker-controlled regular file, where a program expected to create one.
When set to “0”, writing to regular files is unrestricted.
When set to “1” don’t allow O_CREAT open on regular files that we don’t own in world writable sticky directories, unless they are owned by the owner of the directory.
When set to “2” it also applies to group writable sticky directories.