Documentaton - BLOCKS - BKBEGIN

[BK, DIRTY] = BKBEGIN(BK) Begins a block BK by first checking if it exists. If the block exists, it checks if any input blocks have changed since this block was last executed. It also checks if any input parameters have been changed, added, or removed. If any of these conditions is true, DIRTY is set and the timestamp on the block is updated. BK contains the modified block.

See also: BKINIT(), BKEND(), BKPLUG()