Dracut: What does the rd.lvm.snapshot command line option do?

In the dracut.cmdline manpage, under the deprecated section, it has these old options and their replacements.

rd_LVM_SNAPSHOT
    rd.lvm.snapshot

rd_LVM_SNAPSIZE
    rd.lvm.snapsize

But no actual mention of what exactly these do. I haven't been able to find archived manpages or anything online about the specifics behind these options. So I presume it allows you to boot to a specific snapshot instead of the current root. But which snapshots? Normal or Thin or either? What does the option actually take? The name or some sort of other id? Does it require specific dracut modules? Would booting into a snapshot with an older kernel cause problems? Anything else noteworthy or to be concerned about that I'm not thinking of right now?