anyURI and RFC3986

Hello,
 
at http://www.w3.org/TR/xmlschema11-2/#anyURI the current working draft
for "XML Schema 1.1 Part 2: Datatypes" 
refers to RFC3986 (http://www.ietf.org/rfc/rfc3986.txt
<http://www.ietf.org/rfc/rfc3986.txt> ). In appendix B of RFC 3986, the
syntax for a URI is defined by 
the following regular expression:
 
    ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?
 
However, it looks like using this regular expression for schema
validation will lead to an ambiguity when processing
the value of the namespace attribute of a wildcard which, as of
http://www.w3.org/TR/xmlschema11-1/, may be 
 
namespace = ((##any | ##other) | List of (anyURI
<http://www.w3.org/TR/2006/WD-xmlschema11-2-20060217/datatypes.html#anyU
RI>  | (##targetNamespace | ##local)) )
 
The problem is, that the above regular expression leads to an ambiguity
as it (more specifically, the fragment part (#(.*))?)
matches all of the special values like ##any, ##other, etc.
 
So, how should a schema processor validate anyURI ?
 
Best regards
Uli