HTML API: Add method to replace modifiable text.

[dmsnell]

The HTML API has provided get_modifiable_text() since WordPress 6.5, but it has never provided a method to change the modifiable text for a given token in the document.

It should provide this function to make it possible to safely replace HTML text nodes.

Trac ticket: Core-61617

This patch introduces a new method, set_modifiable_text() to the Tag Processor, which makes it possible and safe to replace text nodes within an HTML document, performing the appropriate escaping.

This method can be used in conjunction with other code to modify the text content of a document, and can be used for transforming HTML in a streaming fashion.

get_updated_html() might need this adjustment:

		if ($this->get_token_type() === '#tag') {
			$this->bytes_already_parsed = $before_current_tag;
		}

Without it, replacing a longer string with a shorter one can make $this->bytes_already_parsed negative.

get_updated_html() might need this adjustment:

Thanks @adamziel - this level of review is so helpful! Unfortunately, when I added a test to try and trigger the condition, I couldn't. What do you think? Do you see any problem with this?

​https://github.com/WordPress/wordpress-develop/pull/7007/files#diff-ef817e9b61dcdc18d5e1a84bfbb55370916b179cfed01eab03121456d7ce847cR42-R86

[dmsnell]

In 58829:

HTML API: Add set_modifiable_text() for replacing text nodes.

This patch introduces a new method, set_modifiable_text() to the
Tag Processor, which makes it possible and safe to replace text nodes
within an HTML document, performing the appropriate escaping.

This method can be used in conjunction with other code to modify the
text content of a document, and can be used for transforming HTML
in a streaming fashion.

Developed in ​https://github.com/wordpress/wordpress-develop/pull/7007
Discussed in https://core.trac.wordpress.org/ticket/61617

Props: dmsnell, gziolo, zieladam.
Fixes #61617.

Merged in [58829]
​https://github.com/wordpress/wordpress-develop/commit/c6aaf0a7db6e0555ac61b96cecb699b850fb3187

Thanks @adamziel - this level of review is so helpful! Unfortunately, when I added a test to try and trigger the condition, I couldn't. What do you think? Do you see any problem with this?

That test looks good. I'd also check for regular tags like DIV and then for HTML comments. I ran into that in ​https://github.com/adamziel/site-transfer-protocol, although now can't find the commit where I did it. Eventually I've switched to ​a different method of setting modifiable text, and now I'm happy to migrate to this now that it's merged.

@adamziel if you ever find this problem again I'll be happy to fix it ASAP