7.6.2.2125
REFILL
 
BLOCK EXT
 
( -- flag )

Extend the execution semantics of 6.2.2125 REFILL with the following:

When the input source is a block, make the next block the input source and current input buffer by adding one to the value of BLK and setting >IN to zero. Return true if the new value of BLK is a valid block number, otherwise false.