Purpose of ipv4.dns-option in nmcli

dns-options can be changed for connection name myname to the value value using nmcli con modify myname ipv4.dns-options value Using interactive mode, I get a short description of what dns-options does. nmcli> describe ipv4.dns-options === [dns-options] === [NM property description] Array of DNS options. NULL means that the options are unset and left at the default. In this case NetworkManager will use default options. This is distinct from an empty list of properties. **Question**: What are the value of dns-options field and what is the purpose of dns-option?