docs: function validate(cmd, args, info) {
    AbstractCommand.prototype.validate.apply(this, arguments);
  
    var source = '' + args[0]
      , destination = '' + args[1];
  
    if(!info.db.getKey(args[0], info)) {
      throw NoSuchKey;
    }else if(source === destination) {
      throw SourceDestination;
    }
    args[0] = source;
    args[1] = destination;
  }