Clarify how the primitives solve "client side include feature for HTML" (#2791)

[johannesodland]

The start of the readme.md states that these primitives adresses #2791 Client side include feature for HTML.

HTML primitives for updating parts of a document without a full page refresh Addresses whatwg/html#2142 and whatwg/html#2791 in a unified manner.

If I understand it correctly, this would require support for loading the template from another html document/fragment using the patchsrc attribute.

Would it be possible to add an example explaining how this would work?
Would it be something like this?

<?marker name="navigation">
<template for="navigation" patchsrc="./navigation.html">

I also noticed that the patchsrc is mentioned under "DOM Parts integration". Should it be listed under "Potential enhancement"?

There is also a comment in the feedback from @jakearchibald that states that "Not pursuing patchsrc atm.". Does that mean that the client side include feature is no longer pursued?

[noamr]

The primitives being upstreamed to the HTML standard currently don't address client side includes, but potentially set the stage for it later.
We should update the explainer to be clearer about that as it has changed while working on incubation.

[johannesodland]

That would be helpful. Thank you 🙏

(Sorry for editing while you were answering. I managed to hit the shortcut for creating the issue halfway through 😅).

[noamr]

See #98. Also #95 is an interesting issue where we discussed how this can be extended to support sanitized client-side includes.