Ignoring parts of stat(2)

[grarpamp]

How do I make rsync ignore and not report or update certain parts
of the [l]stat(2) struct or checksum when selecting which items to
report or update in a hierarchy?

For example, I want to run:
 rsync -Haxi --delete /hier1/ /hier2/
and have it NOT do anything if say ONLY the modtime differs.
Leaving out or in the --times [-t] option from the expansion of -a
to -rlptgoD obviously does not do this.

That would be a pretty awesome feature to have :)
Especially for where modtime is the only thing changed. Commonly
caused by someone extracting a cp/tar/cpio/etc without preserving
the modtime in particular.

I would think the new ignore option bits would apply easily to at
least the following fields:

size [block or bytes]
perms [ideally and optionally modified by some supplied ignore/watch mask]
user
group
timestamp [birth/mod/access/change where applicable]
flags
checksum

Comments on this?