[TAKAHASHI Makoto]

http://www.w3.org/TR/1999/REC-html401-19991224/types.html#h-6.2

says

ID and NAME tokens must begin with a letter ([A-Za-z])
and may be followed by any number of letters, digits
([0-9]), hyphens ("-"), underscores ("_"), colons
(":"), and periods (".").

awstats.pl

• my $regtruncanchor=qr/#(\w*)$/;
• my $regtruncanchor=qr/#([A-Za-z][A-Za-z0-9-_:.]*)$/;