[CSS21] Backslash in uri()

Hi,

In "4.3.4 URL + URN = URI" of CSS21, there is such paragraph:

Parentheses, commas, whitespace characters, single quotes (') and double
quotes (") appearing in an unquoted URI must be escaped with a
backslash: '\(', '\)', '\,'.

Shouldn't backslash itself be included in the must-be-escaped list?

Isn't it better example list to include all these characters (incl.
whitespace, single quotes and double quotes)?

Regards,
ogi