> Do you have a suggestion or an example of how this might be used?

The idea I have in my head isn't backwards compatible, but I was thinking of something like

haproxy:(tls:hostname.example:endpoint=(tcp:7.6.5.4:443))

This would break any endpoint description that starts with `(` but allows arbitrarily nested endpoints (or even just date containing `:`).

Thinking about it some more, there isn't currently any endpoint descriptions that have an empty name, so we could have a entirely new syntax that starts with `:`. If we went in that direction, we'd definitely want to think about future extensibility when designing it.