This procedure only applies when invoked by another procedure.
This mapping procedure imposes the following constraints on a send string.
The right hand operand must be a single literal bit (0/1/L/H), or a reference to such a string..
The left hand operand must recognize a single bit of any value, or be a reference to such a string.
The send string is mapped to a pad bit. The encoding is a single bit. An encoder shall encode the literal bit specified by the right hand operand. A decoder shall accept any bit value.