RFC: Does ZFS block cloning do this?

Hi,

NFSv4.2 has a CLONE operation. It is described as doing:
   The CLONE operation is used to clone file content from a source file
   specified by the SAVED_FH value into a destination file specified by
   CURRENT_FH without actually copying the data, e.g., by using a
   copy-on-write mechanism.
(It takes arguments for 2 files, with byte offsets and a length.)
The offsets must be aligned to a value returned by the NFSv4.2 server.
12.2.1.  Attribute 77: clone_blksize

   The clone_blksize attribute indicates the granularity of a CLONE
   operation.

Does ZFS block cloning do this?

I am asking now, because although it might be too late,
if the answer is "yes", I'd like to get VOP calls into 15.0
for it. (Hopefully with the VOP calls in place, the rest could
go in sometime later, when I find the time to do it.)

Thanks in advance for any comments, rick