'Refit (normalize) the attribute\'s value.
@param a: An attribute.
@type a: L{Attribute}'

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)))
