fetch-event-source VS WHATWG HTML Standard

* `text/event-stream` relies on a modified version of [Azure's fetch-event-source](https://github.com/Azure/fetch-event-source). They handle errors and chunking better than I was. New version has been tested out to 4 billion fragments rendered on a single page with no errors.

The EventSource Web API for handling SSEs (built into most modern browsers) unfortunately supports only GET requests, which was quite limiting when a POST request with larger body JSON data was required. As an alternative, you can use the Fetch API or a ready library like Microsoft’s Fetch Event Source.

Aforementioned limitations are taken care with a specialised SSE client (inspired by the awesome @microsoft/fetch-event-source) and two separate connection modes: the HTTP/1 safe "single connection mode" that uses a single SSE connection for receiving events with separate HTTP requests dictating the behaviour, and the HTTP/2+ "distinct connections mode" that uses distinct SSE connections for each GraphQL operation, accommodating the parameters in the request itself.

WHAT-WG HTML

There's a long-standing WHATWG feature request open for it here: https://github.com/whatwg/html/issues/2791

And several userland custom element implementation, like https://www.npmjs.com/package//html-include-element

One of the cool things that you can do with client-side includes and shadow DOM is render the included HTML into a shadow root that has s, so that the child content of the include element is slotted into a shell implemented by the included HTML.

This lets you do things like have the main page be the pre-page content and the included HTML be a heavily cached site-wide shell, and then another per-user include with personalized HTML - all cached appropriately.

The `allow` attribute on iframes is a relatively recent API addition from 2017

https://github.com/whatwg/html/pull/3287

I think there's a pretty strong argument at this point for this kind of replacing DOM with a response behavior being part of the platform.

I think the first step would be an element that lets you load external content into the page declaratively. There's a spec issue open for this: https://github.com/whatwg/html/issues/2791

And my custom element implementation of the idea: https://www.npmjs.com/package/html-include-element

Then HTML could support these elements being targets of links.

> Consider https://www.ietf.org/rfc/rfc1866.txt vs https://html.spec.whatwg.org/multipage/

I thought, oh, that's not so bad. Then I realized what I was looking at was a 10 page index.

I'd love to see something like HTMX get standardized, but I'm extremely pessimistic for HTMX's prospects for standardization in HTML.

In talking to a few standards folks about it, they've all said, "oh, yeah, you want declarative AJAX; people have tried and failed to get that standardized for years." Even just trying to get

to target a section of the page that isn't an has been argued about and hashed out for years.<p>Why is that? Well, for example, here's the form you have to fill out to start standardizing a front-end feature. <a href="https://github.com/whatwg/html/issues/new?assignees=&labels=addition%2Fproposal%2Cneeds+implementer+interest&projects=&template=1-new-feature.yml">https://github.com/whatwg/html/issues/new?assignees=&labels=...</a><p>It asks three main questions:<p>* What problem are you trying to solve?

The issue with a single global event handler is discussed here: https://github.com/WICG/close-watcher#a-single-event

If you use popover="", you get the kind of functionality you're discussing for free. For

, the discussion is in progress and reaching a conclusion: https://github.com/whatwg/html/issues/9373