io.1
This source file defines all the input / output words within the Forth kernel.
bs
( --- n1 )
This constant returns the ASCII code for the backspace character.
bl
( --- n1 )
This constant returns the ASCII code for the space character.
>in
( --- n1 )
This variable (pronounced "to in") returns the current position within the input stream (how far into it we have parsed).