Make Context and public methods either open or turn them into a protocol.

[kaygro]

This would enable more substantial extensions, without people bothering you about modifications, which aren't really relevant to your project goals. It might also be a good thing to open up the default tags in a similar fashion.

[mrackwitz]

I like this idea, as I happen to need a lazy context at the moment.
Either way this will enlarge the public API and so add burden from a maintainers perspective. Subclassing isn't quite en vogue with Swift and tends to be harder to get right. I'd tend towards protocols, if it doesn't complicate things too much.
@kylef @AliSoftware @ilyapuchka: Any opinions on that? I'd be open to tackle this.
Also open for alternatives, if you have ideas.

[AliSoftware]

\cc @djbe