:DESPATCH

  /edit?node=(\w+);... { 
      print "You're trying to edit '$node'"; 
    }; 

:PARAM

  node  {
    my ( $node ) = @_;
    my $db = My::Database->new(...);
    return $node if $db->selectValue( sql => "select count(*) from nodes where node=?", param => [$node] );
    print "invalid node: $node";
    return undef;
  }