Openwrt Define DNS servers with dhcp option 6

In this forum example, it is used for VPN forum.openwrt.org/t/wireguard-vpn-not-working/166385/14
In another forum example a custom gateway is defined for a specific host for testing. forum.openwrt.org/t/conditional-dhcp/70441/8
The main docs has more examples openwrt.org/docs/guide-user/base-system/dhcp_configuration