sub fix_umlaut
{
    my ( $tagname, $attr, $text ) = @_;
    $output .= $text;
    if ( $tagname eq 'idx:orth' and $$attr{value} =~ s/[$um]/$replace{$1}/g ) {
        delete $$attr{'infl'};
        $output .= '<idx:orth ' . map( " $_=\"".$$attr{$_}.'"',keys(%$attr)) . '/>';    # repeat the tag with modified umlauts
    }
}