bless is used to modify the volume bootability characteristics of filesystems, as well as select the active boot volume. bless has 5 modes of execution: Folder Mode, Mount Mode, Device Mode, NetBoot Mode, and Info Mode.
However, one has to take care not to add too much crap as the booter needs to absolutely stay within a 64k real mode code segment with the code being loaded at offset 0x200 (512 bytes) in that segment. That means the limit is 63.5k but then there is cdboot which is a 2k stub-booter followed by the real booter thus effectively meaning you can have at most 62k of code. The project as shipped is in the high 50k and my changes have already added another k or two. Not much more can be added before the whole thing would have to be rewritten to handle loading a third booter and/or loading the rest of itself which would just be ludicrous.
