Documentaton - BLOCKS - BKFETCH

BK = BKFETCH(BK) returns BK unchanged.

BK = BKFETCH(TAG) returns the block BK corresponding to TAG.

VAL = BKFETCH(BK, PROP) loads the property PROP of the block BK. The properties that can be fetched depend on the block type. BKFETCH(TAG, PROP) also loads the property PROP, but first reads the block from disk.

BKFETCH(BK, PROP, ARG1, ARG2, ...) passes additional arguments to the block to specify the property to be fetched.

[VAL1, VAL2, ...] = BKFETCH(...) is used when multiple values need to be returned.