code: def refitValue(self, a):
          
          p, name = splitPrefix(a.getValue())
          if p is None:
              return
          ns = a.resolvePrefix(p)
          if self.permit(ns):
              u = ns[1]
              p = self.prefixes[u]
              a.setValue(':'.join((p, name)))
docs: Refit (normalize) the attribute's value.
          @param a: An attribute.
          @type a: L{Attribute}