scsh name	Posix ctype	Alternate
-----------------------------------------
lower-case	lower
upper-case	upper
alphabetic	alpha
numeric		digit		num
alphanumeric	alnum		alphanum
punctuation	punct
graphic		graph
blank					    (Gnu extension)
whitespace	space		white	    ("space" is potentially confusing.)
printing	print
control		cntrl
hex-digit	xdigit		hex
ascii		ascii			    (Gnu extension)

SRE ::= ... <char-class> ...

<char-class> ::= <char>
	       | any | nonl | <class-name>
	       | (in     <char-class-arg> ...)
	       | (not-in <char-class-arg> ...)
	       | (and    <char-class-arg> ...)
	       | (diff   <char-class-arg> ...)
	       | (- <char-or-string> ...)
	       | ,<cset-exp>

<char-class-arg> ::= <char-class> | <string>



(diff <arg1> <arg2> ...) = (and <arg1> (not-in <arg2> ...))

~!@#$%^&*-_+=|:<>?/ in 

(: ...) sequence

(and ...)
(or ...)
(not ...)
(diff ...)

(* ...)
(+ ...)
(- ...)

(in ...)	; union
(not-in ...)    ; complement-of-union
(and ...)	; intersection
(diff ...)	; diff

(+ ...)		; union
(~ ...)		; complement-of-union
(& ...)		; intersection
(- ...)		; diff

(in ...)	; union
(~ ...)		; complement-of-union
(& ...)		; intersection
(- ...)		; diff
