VAX Operands
------------

   The immediate character is `$' for Unix compatibility, not `#' as
DEC writes it.

   The indirect character is `*' for Unix compatibility, not `@' as DEC
writes it.

   The displacement sizing character is ``' (an accent grave) for Unix
compatibility, not `^' as DEC writes it.  The letter preceding ``' may
have either case.  `G' is not understood, but all other letters (`b i l
s w') are understood.

   Register names understood are `r0 r1 r2 ... r15 ap fp sp pc'.  Any
case of letters will do.

   For instance
     tstb *w`$4(r5)

   Any expression is permitted in an operand.  Operands are comma
separated.