//// Copyright (c) 2012, Brian Frank and Andy Frank// Licensed under the Academic Free License version 3.0//// History:// 09 Mar 12 Brian Frank Creation//**** UnknownKeyErr indicates an attempt to lookup a non-existent key.**const class UnknownKeyErr : Err {**** Construct with specified error message and optional root cause.**new make(Str msg := "", Err? cause := null) }