The SOR$DTYPE routine defines a key data type that is not
    normally supported by SORT/MERGE. (This routine is not currently
    supported by the high-performance Sort/Merge utility.) This
    routine returns a key data type code that can be used in the key_
    buffer argument to SOR$BEGIN_SORT or SOR$BEGIN_MERGE to describe
    special key data types (such as extended data types and National
    character set (NCS) collating sequences).

    Format

      SOR$DTYPE  [context] ,dtype_code ,usage ,p1