# File lib/openid/extensions/ax.rb, line 97
    def self.to_type_uris(namespace_map, alias_list_s)
      return [] if alias_list_s.nil?
      alias_list_s.split(',').inject([]) {|uris, name|
        type_uri = namespace_map.get_namespace_uri(name)
        raise IndexError, "No type defined for attribute name #{name.inspect}" if type_uri.nil?
        uris << type_uri
      }
    end