Chapman Flack <flack@cerias.purdue.edu> writes:

> I'd still be really interested in seeing what direction the Single UNIX Spec
> is taking on these issues; I haven't had time to really look yet.

I just checked SUSv3.  It says nothing particularly useful.

Filenames:

"For a filename to be portable across implementations conforming to
 IEEE Std 1003.1-2001, it shall consist only of the portable filename
 character set as defined in Portable Filename Character Set.

 The hyphen character shall not be used as the first character of a
 portable filename.  Uppercase and lowercase letters shall retain
 their unique identities between conforming implementations.  In the
 case of a portable pathname, the slash character may also be used."

Portable Filename Character Set:

"The set of characters from which portable filenames are constructed.

 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
 a b c d e f g h i j k l m n o p q r s t u v w x y z
 0 1 2 3 4 5 6 7 8 9 . _ -

 The last three characters are the period, underscore, and hyphen
 characters, respectively."

Ian