HTMX 4 support

[Cyberbeni]

There is a new htmx major version currently in alpha.

The SSE extension will be part of the main project but it seems like part of it, for example sse-swap, is still missing: bigskysoftware/htmx#3519 (edit: probably hx-swap-oob is the replacement) (edit2: there is also this partial update thing that just seems like a duplicate of OOB swap? https://github.com/bigskysoftware/htmx/blob/f3953b29b0c4f5c4225c313972ace3ef9b24de52/src/htmx.js#L1249 )

There is this new hx-stream attribute: https://four.htmx.org/docs/#stream-modes

I don't think setting up configuration through a meta tag is new but that's currently not part of elementary-htmx, it would be nice to have autocompletion for that too, instead of having to pass a huge string for the meta tag's content: https://four.htmx.org/docs/#configuration

I was thinking maybe package traits (introduced in Swift 6.1) could be used, so that we wouldn't need to maintain multiple branches for supporting multiple versions of htmx (The current version of htmx will still remain supported, v4 will not even become the latest for at least a year after it's initial release). Traits would probably be also useful for enabling the different extensions, so people only have to import the ElementaryHTMX target and we would also only have a single configuration type that only included the configurations that are relevant for the selected extensions.

Edit 3: seems like the API is still actively being changed

[sliemeobn]

thanks for bringing this up. I think it is a bit early to commit to anything (as the htmx 4 API is still firming up), but it can't hurt to think through how to support this in the future.

I am not 100% convinced that traits are a great fit for this (as ideally one can enable multiple traits, or "all of them"). but maybe they are still the best tool for the job? I guess it depends on how "compatible" the API surface remains in htmx... 🤔