The definition of a Character Range includes EBNF grammar rules [17] to [22] 
and some prose, which says:

A single XML character is a character range that identifies the set of 
characters containing only itself. All XML characters are valid character 
ranges, except as follows:

The [, ], and \ characters are not valid character ranges; 
The ^ character is only valid at the beginning of a positive character group if 
it is part of a negative character group; and 
The - character is a valid character range only at the beginning or end of a 
positive character group. 
The last item contradicts production [17] of the grammar.

See http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2001Sep/0045.html