append_ipset() {
    if [ -x /sbin/fw4 ]; then
        local domainlist=${1%/*}
        local setlist=${1##*/}
        local nftsets=""

        IFS=,
        for set in $setlist; do
            local family=$(nft -t list set inet fw4 "$set" 2>&1 | sed -nre 's#^\t\ttype .*\bipv([46])_addr\b.*$#\1#p')

            [ -n "$family" ] || \
                logger -t dnsmasq "Cannot infer address family from not existing nftables set '$set'"

            nftsets="${nftsets:+$nftsets,}${family:+$family#}inet#fw4#$set"
        done
        IFS=$' \t\n'

        xappend "--nftset=$domainlist/$nftsets"
    else
        xappend "--ipset=$1"
    fi
}