The extended syntax of #, as indicated by the subsequent character, with
  questionable or not-yet-fully worked-out cases indicated by "???", and *
  in column 1 meaning NIL/NIL-compatibility only

*    "		BITS expressed as 4 bits per hexadecimal digit
     %		MACROEXPAND following form at read time.
     '		Like single-quote macro.  #'foo  ==>  (FUNCTION foo)
*    (		S-expression VECTOR, elements inside list
     * 		Unsigned-integer, or Machine-word
     +		Conditional read, for next expression.  A feature name, or 
		list with "OR" or "AND" as first element and remaining elements
		as feature names, must immediately follow.  Next form is
		skipped unless this system has one of the requested features
		(for "OR") or unless it has all the requested features (for 
		"AND".
     , 		Load-time evaluation
     -		Conditional read, like "#+", but next form is skipped if the
		conditions indicated are satisfied.
     . 		Read-time evaluation
     0 ... 9	decimal representation for a radix denotation
     : 		Flush a package prefix, e.g.  #:SI:FOO  is the same as FOO
*    =		a CHARACTER denoted by its numerical code value as a fixnum
		(e.g.  #=38 is "&"), or a FIXNUM denoted by the CHARACTER 
		which has that code (e.g. #=~& is 38).
???  ?		Illegal object (cannot be read in, but useful for debug print)
*    B 		Binary notation for a bitstring follows
*    I		Numerical indeterminancy (#^I), positive infinity (#^+) and
		negative infinity (#^-).  Possibly an unsigned infinity too.
*    L		Labeling notation,  #Lfoo= sets, and #Lfoo#  references
     M		Next form is flushed unless this is a MACLISP system
     N		Next form is flushed unless this is a NIL system
     O		Octal notation follows, either for a number or for a bitstring
     Q 		Next form is flushed unless this is a LISPM system
*    T 		Truthity, a specific non-null, not false, constant
     X		Hexadecimal notation for a number or for a bitstring
     / 		A FIXNUM denoted by the next character (e.g.  #/& is 38).
     \ 		A FIXNUM denoted by the following standard symbolic name
		(e.g.  #\SP  for 32., and #\RUBOUT for 127.)
???  [		ARRAY   ???
     ^		Machine dependent control character.
*    { 		An EXTEND used as a class object.