BIND 9.16.12 is missing the full documentation pieces for back-ported option max-ixfr-option

Specifically, I couldn't find the option grammar, so had no idea of the syntax and that 'unlimited' can be used (which essentially reverts the behaviour to as it was before this option was created).

Additionally, I don't know (in either 9.16 or 9.17, if I can set a percentage greater than 100, and/or what happens if I set the percentage to 0 (which I assume is the equivalent of disabling outbound IXFRs).

Please fix!

(I've tagged this as Customer because I was researching how to use the option on behalf of a specific customer in order to respond with advice on their support ticket)