public override string ToString ()
{
int count = Count;
if (count == 0)
return "";
StringBuilder sb = new StringBuilder ();
string [] keys = AllKeys;
for (int i = 0; i < count; i++) {
sb.AppendFormat ("{0}={1}&", keys [i], this [keys [i]]);
}
if (sb.Length > 0)
sb.Length--;
return sb.ToString ();
}
}