When I saw the title about "TLS Callbacks", I immediately knew what kind of TLS the article was talking about. But then when I saw the comment on ERR_SSL_VERSION_OR_CIPHER_MISMATCH – at the time there weren't many others – and I started to doubt myself – has TLS the network protocol added some new feature called "callbacks" that I'm unfamiliar with?

Some libraries use callbacks for e.g. host certificate verification so the consuming application can manage its own whitelists.

I figured but erred on the side of "maybe not a joke" :D