Add a render element for hx-partial

Problem/Motivation

HTMX 4 processes a custom tag that is meant to enclose an HTML fragment rendered for insertion into an existing page.

<hx-partial hx-target="#messages" hx-swap="beforeend">
    <div class="message">New message content</div>
</hx-partial>

tags can have the following attributes:

hx-target - CSS selector for where to place content
id - Shorthand alternative to hx-target. Targets the element with that ID (e.g. targets #messages)
hx-swap - Optional. Swap style (defaults to innerHTML)

Upstream documentation: hx-partial.

Proposed resolution

Create a render element plugin for hx-partial with variables for content, target and swap.

Remaining tasks

User interface changes

none

Introduced terminology

none

API changes

New render element

Data model changes

none

Release notes snippet