6.1.2216
SOURCE
 
CORE
 
( -- c-addr u )

c-addr is the address of, and u is the number of characters in, the input buffer.

Rationale:
SOURCE simplifies the process of directly accessing the input buffer by hiding the differences between its location for different input sources. This also gives implementors more flexibility in their implementation of buffering mechanisms for different input sources. The committee moved away from an input buffer specification consisting of a collection of individual variables.
Testing:
: GS1 S" SOURCE" 2DUP EVALUATE >R SWAP >R = R> R> = ;
T{ GS1 -> <TRUE> <TRUE> }T

: GS4 SOURCE >IN ! DROP ;
T{ GS4 123 456 
    -> }T