DESCRIPTOR DEFINITION

$NNNCCC,TF,LF,FLAG
    This item introduces the definition of a descriptor,
         where:

    NNN  - descriptor identifier (octal tag)
           The tags are defined in numerical order. (see ';')

    CCC  - descriptor name (IMP type name).

    IF   - TYPE<<4+FORM

             TYPE               FORM

         0 - GENERAL       0 - UNDEFINED
         1 - INTEGER       1 - SIMPLE    (E.G. INTEGER)
         2 - REAL          2 - NAME      (E.G. INTEGERNAME)
         3 - STRING        3 - LABEL
         4 - RECORD        4 - FORMAT
                           5 - UNDEFINED
                           6 - SWITCH
                           7 - ROUTINE
                          10 - FUNCTION
                          11 - MAP
                          12 - PREDICATE
                          13 - ARRAY
                          14 - ARRAYNAME
                          15 - NAMEARRAY
                          16 - NAMEARRAYNAME
                          17 - UNDEFINED

    LF       - STRINGS : MAXIMUM LENGTH (ZERO = NONE GIVEN)
             - RECORDS : FORMAT TAG     (ZERO = NONE GIVEN)
             - OTHER   :   1 - DEFAULT SIZE
                           2 - BYTE
                           3 - SHORT
                           4 - LONG

    FLAG - SCOPE + SPEC<<3 + PROT<<4 + EXTRA<<8

         SCOPE           SPEC          PROT

         0 - NULL        0 - NO SPEC   0 - NONE
         1 - OWN         1 - SPEC     &1 - FROZEN...
         2 - CONSTANT                 &2 - ..FROZENNAME
         3 - EXTERNAL                 &4 - ..ARRAYFROZENNAME
         4 - SYSTEM
         5 - DYNAMIC               EXTRA - FORM DEPENDENT
         6 - PRIMITIVE (PRIM)
         7 - PERMANENT (PERM)

  @tag   Stack a copy of the descriptor with identifier tag.
         (see RECORDS for negative tag)



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