Is NFSv4.2's clone_blksize per-file or per-file-system?

Hi,

I'm looking at RFC7862 and I cannot find where it
states if the clone_blksize attribute is per-file or
per-file-system.

If it is not in the RFC, which do others think it is?
(Or maybe, if you have implemented CLONE,
which does your implementation assume?)

In case you are wondering why I am asking,
it turns out that files in a ZFS volume can have
different block sizes. (It can be changed after the
file system is created.)

Thanks, rick