The HTML Processor internally throws an exception when it reaches HTML
that it knows it cannot process, but this exception is not made
available to calling code. It can be useful to extract more knowledge
about why it gave up, especially for debugging purposes.
In this patch, more context is added to the WP_HTML_Unsupported_Exception
and the last exception is made available to calling code through a new
method, `get_unsupported_exception()`.
Developed in https://github.com/WordPress/wordpress-develop/pull/6985
Discussed in https://core.trac.wordpress.org/ticket/61646
Props bernhard-reiter, dmsnell, jonsurrell.
See #61646.
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This patch introduces the //first// of //many// iterations on the evolution of the HTML API, the HTML Processor, which is built in order to understand HTML structure including nesting, misnesting, and complicated semantic rules.
In the first iteration, the HTML Processor is arbitrarily limited to a minimal subset of functionality so that we can review it, ship it, test it, and collect feedback before moving forward. This means that this patch is more or less an extension to the Tag Processor query language, providing the ability not only to scan for a tag of a given name, but also to find an HTML element in a specific nesting path.
The HTML Processor also aborts any time it encounters:
- a tag that isn't a `P`, `DIV`, `FIGURE`, `FIGCAPTION`, `IMG`, `STRONG`, `B`, `EM`, `I`, `A`, `BIG`, `CODE`, `FONT`, `SMALL`, `STRIKE`, `TT`, or `U` tag. this limit exists because many HTML elements require specific rules and we are trying to limit the number of rules introduced at once. this work is targeted at existing work in places like the image block.
- certain misnesting constructs that evoke complicated resolution inside the HTML spec. where possible and where simple to do reliably, certain parse errors are handled. in most cases the HTML Processor aborts.
The structure of the HTML Processor is established in this patch. Further spec-compliance comes through filling out //more of the same// kind and nature of code as is found in this patch. Certain critical HTML algorithms are partially supported, and where support requires more than is present, the HTML Processor acknowledges this and refuses to operate.
In this patch are explorations for how to verify that new HTML support is fully added (instead of allowing for partial updates that leave some code paths non-compliant). Performance is hard to measure since support is so limited at the current time, but it should generally follow the performance of the Tag Processor somewhat close as the overhead is minimized as much as practical.
Props dmsnell, zieladam, costdev.
Fixes#58517.
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