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noamr merged 1 commit into from
Jan 8, 2026
Merged

Add option for marker nodes with start/end attributes #77

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54 changes: 54 additions & 0 deletions patching-explainer.md
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Expand Up @@ -204,6 +204,60 @@ The patches uses a single marker node:

</details>

##### Markers with start/end attributes

This alternative adds `start` and `end` boolean attributes to the marker nodes, so that the start/end of a range are defined by the markers, not attributes on `<template>`.

This makes it possible to replace a `<title>` element.

<details>
<summary>Example</summary>

```html
<head>
<?marker name="metadata" start?>
<title>Page 1</title>
<?marker name="metadata" end?>
</head>

<template contentname="metadata">
<title>Page 2</title>
</template>
```

</details>

Details around `<title>` and the RCDATA tokenizer state are the main reason that the tag name needs to be repeated in other alterantives, but this isn't needed in this option, the children of `<template>` elements are just the new content. The `contentname` attribute can refer to either marker node(s) or an element.

When `start` and `end` aren't used, the marker node is replaced. The interleaved patching example then becomes:

<details>
<summary>Example</summary>

```html
<template contentname=search-results>
<p>first result</p>
<!-- add markers to allow for "append" -->
<?marker name=search-results-more?>
</template>

<template contentname=product-carousel>
Actual carousel content
</template>

<template contentname=search-results-more>
<p>second result</p>
<!-- new markers are needed for the next "append". -->
<?marker name=search-results-more?>
</template>

<template contentname=search-results-more>
<p>third result</p>
</template>
```

</details>

## Script-initiated patching

`streamHTMLUnsafe()` is being pursued as a [separate proposal](https://github.com/whatwg/html/issues/2142), but will also work with patching. When `<template contentmethod>` appears in the streamed HTML, those patches can apply to descendants of element on which `streamHTMLUnsafe()` was called.
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