What does a rmlint's "clone" for btrfs do?

I was reading the [rmlint](http://rmlint.readthedocs.io/en/latest/index.html#) manual, and one of the duplicate handlers are clone and reflink: >· clone: btrfs only. Try to clone both files with the BTRFS_IOC_FILE_EXTENT_SAME ioctl(3p). This will physically delete duplicate extents. Needs at least kernel 4.2. > >· reflink: Try to reflink the duplicate file to the original. See also --reflink in man 1 cp. Fails if the filesystem does not support it. What exactly does this clone do, and how is it different from a reflink? What does the BTRFS_IOC_FILE_EXTENT_SAME ioctl do?