Document supported matrix versions, and introduce compatibility modes for older ones

[ShadowJonathan]

Your use case

What would you like to do?

• Document the matrix versions supported ("Compatible with matrix vX" badges/shields#7245)
  • Document this within the client
• Introduce compatibility probing (call /versions)
  • Show user-facing error when server and client supported versions mismatch
    ("Cannot communicate with server, your client supports versions v1.1 and v1.2, but the server only supports v1.0")
• Introduce compatibility modes based off of the /versions response for older versions

Why would you like to do it?

Matrix now has a quarterly release cadence, it'd be nice to make element compatible with older matrix versions in a easily understandable way. (So that users may check compatibility for themselves)

Have you considered any alternatives?

No response

Additional context

No response

[pixlwave]

Hi @ShadowJonathan, I'm not really sure what actions we can take from this other than adding a note to the README that we currently support Matrix v1.0. We already have an issue for Matrix 1.1 #5005 (which simply links to the web one for now), with detailed information on the changes to be made.

[ShadowJonathan]

@pixlwave sorry, this would actually be more an SDK issue, and it's a request for future aspiration, in the following way;

• introduce compatibility behaviour when dealing with older servers, such as disabling certain routes or functionality until that server denotes it supports it (i.e. with a new version)
• Enumerate and document when certain features or API calls are first introduced, or are changed according to matrix compatibility, so that above can apply.