Perhaps need structured ALPN tokens

[grmocg]

There has been a lot of conversation about how to use the ALPN tokens.
In the case of TLS, the token indicates only the application-layer protocol on top of TLS/TCP/IP. This is unlikely to lead to a combinatorial explosion of IDs.

In the case of usage from DNS, the token potentially indicates a stack of protocols.
This could easily lead to a combinatorial explosion of IDs, especially if identifiers for schemes are included.

If it is decided that this is unnecessary, then some characters should be reserved so that structured tokens can be created in the future, e.g. '/', '{', '}', ',' could be reserved.

[mnot]

Discussed in London; constraining ALPN tokens formally isn't in-scope for this WG, but we'll endeavour not to use special characters.