7.6.1.2400
UPDATE
 
BLOCK
 
( -- )

Mark the current block buffer as modified. An ambiguous condition exists if there is no current block buffer.

UPDATE does not immediately cause I/O.

See:
7.6.1.0800 BLOCK, 7.6.1.0820 BUFFER, 7.6.1.1559 FLUSH,
7.6.1.2180 SAVE-BUFFERS.