I agree that it should be voluntary, but it seems like a core-library-level function that we should be offering in our NDK package, even if it's a separate repo/tool.

It's data validation will be beyond the abilities of many people using our NDK to build. You see how many apps just accept any garbage. 

 Totally cool with that yeah, just having tools available for developers to choose to filter/moderate content within their clients to offer some protection from rogue relays. I kind of like that too I suppose. It gives client devs the ability to pass that power to the user if they choose.