(IMMEDIATE#) (FORGET) (KEY)
(IMMEDIATE#) ( -- bit-mask )  
<PFE-SMART>
returns the bit-mask to check if a found word is immediate 
    " my-word" FIND IF >FFA C@ (IMMEDIATE#) AND 
                       IF ." immediate" THEN ELSE DROP THEN

reference: p4_immediate_bit in ../src/yours.c:0100, export CO (IMMEDIATE#)