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sub devices_for {
    my ( $thing ) = @_;
    my @subs = query( $thing );
    return map { /^DEVICE\d+/ ? $_ : devices_for( $_ ) } @subs;
}

sub devices_for {
    my ( $thing ) = @_;
    return $thing if $thing =~ /^DEVICE\d/;
    return map { devices_for( $_ ) } query( $thing );
}

sub devices_for {
    return ( $_[0] =~ /^DEVICE\d/ )
        ? $_[0]
        : map { devices_for( $_ ) } query( $_[0] );
}