if ( C4::Context->preference('SummaryHoldings') && !@$itemnumbers ) {

        require C4::Holdings;

        my $holdings_fields = C4::Holdings::GetMarcHoldingsFields( $biblionumber );

        $marc->append_fields(@$holdings_fields) if ( @$holdings_fields );

    }

=head2 GetMarcHoldingsFields

  my @marc_fields = GetMarcHoldingsFields($biblionumber);

Returns an array of MARC::Record objects of the holdings for the biblio.

=cut

sub GetMarcHoldingsFields {

	my ( $biblionumber ) = @_;

    # This is so much faster than using Koha::Holdings->search that it makes sense even if it's ugly.

    my $sth = C4::Context->dbh->prepare( 'SELECT * FROM holdings WHERE biblionumber = ?' );

    $sth->execute( $biblionumber );

    my $holdings = $sth->fetchall_arrayref({});

    $sth->finish();

    my @holdings_fields;

    my ( $holdingstag, $holdingssubfield ) = GetMarcHoldingFromKohaField( 'holdings.holdingbranch' );

    ITEMLOOP: foreach my $holding (@$holdings) {

        my $mungedholding = {

            map {

                defined($holding->{$_}) && $holding->{$_} ne '' ? ("holdings.$_" => $holding->{$_}) : ()

            } keys %{ $holding }

        };

        my $marc = TransformKohaHoldingToMarc($mungedholding);

        push @holdings_fields, $marc->field( $holdingstag );

    }

    return \@holdings_fields;

}

=head2 TransformKohaToMarc

    $record = TransformKohaToMarc( $hash [, $params ] )

This function builds partial MARC::Record from holdings hash entries.

This function is called when embedding holdings into a biblio record.

=cut

sub TransformKohaHoldingToMarc {

    my ( $hash, $params ) = @_;

    my $record = MARC::Record->new();

    SetMarcUnicodeFlag( $record, C4::Context->preference("marcflavour") );

    # In the next call we use the Default holdings framework, since it is considered

    # authoritative for Koha to Marc mappings.

    my $mss = C4::Biblio::GetMarcSubfieldStructure( 'HLD', { unsafe => 1 } ); # do not change framewok

    my $tag_hr = {};

    while ( my ($kohafield, $value) = each %$hash ) {

        foreach my $fld ( @{ $mss->{$kohafield} } ) {

            my $tagfield    = $fld->{tagfield};

            my $tagsubfield = $fld->{tagsubfield};

            next if !$tagfield;

            my @values = $params->{no_split}

                ? ( $value )

                : split(/\s?\|\s?/, $value, -1);

            foreach my $value ( @values ) {

                next if $value eq '';

                $tag_hr->{$tagfield} //= [];

                push @{$tag_hr->{$tagfield}}, [($tagsubfield, $value)];

            }

        }

    }

    foreach my $tag (sort keys %$tag_hr) {

        my @sfl = @{$tag_hr->{$tag}};

        @sfl = sort { $a->[0] cmp $b->[0]; } @sfl;

        @sfl = map { @{$_}; } @sfl;

        # Special care for control fields: remove the subfield indication @

        # and do not insert indicators.

        my @ind = $tag < 10 ? () : ( " ", " " );

        @sfl = grep { $_ ne '@' } @sfl if $tag < 10;

        $record->insert_fields_ordered( MARC::Field->new($tag, @ind, @sfl) );

    }

    return $record;

}

If summary holdings are enabled, 'include_items' includes their location information too.