URLs such as release notes, sumo articles for specific feature etc. are dynamically generated

Services.urlFormatter.formatURLPref(
        "app.support.baseURL"
      )&<static_query_params>

Currently easy to add to local messages: evaluate the expression as part of the message.
Not supported for RS messages.

Do we have a good way to track what firefox versions support what capabilities, e.g., this formatURL or remote l10n? We would need to make sure to target messages to only show up in versions that support them; otherwise, it seems quite easy to accidentally deploy a message that is broken in older firefoxes.

We have the What's New Panel content guide that mentions dynamic URLs starting 72+.
It would be nice to enforce some of these checks similar to how the documentation for our targeting getters is enforced through unit tests.
I think this would be more complicated. The way I see it possible is by landing the RS dumps in m-c and using mochitests to evaluate the messages.
However the usecase for the WNPanel seems to have shifted

No river. Card content will become dated, and we do not want users to depend on WNP as the place they find things

So we might not have the same long term support constraints like for snippets. If this changes we could try enforcing with mochitests.

https://hg.mozilla.org/mozilla-central/rev/74d6833f6173