XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (651 page)

and
#
characters.

A
negative group
(
negCharGroup
) consists of a circumflex
∧
followed by a
positive group
. A negative group matches any character that is not matched by the corresponding positive group. For example, the negative group
[
∧
abc]
matches any character except
a
,
b
, or
c
.

A
subtraction
(
charClassSub
) consists of either a positive group or a negative group, followed by the
-
symbol, followed by a character class expression (which, as we saw earlier, is a character group enclosed in square brackets). A subtraction matches any character that matches the group preceding the
-
operator, provided it does not also match the character class expression following the
-
operator. For example,
[0-9-[5]]
matches any digit except
5
.