Custom element with both value and type attributes throws an unknown error - any way to handle?

[Jamie452]

Our use case led us to use rehype to parse HTML, perform transformations, and then output back into HTML.

Rehype has worked great so far, but we've just tried inputting a custom HTML element, which has both type and value attributes and are hitting the following error.

Input:

<my-custom-tag type="some type" value="some value"></my-custom-tag>

Error:

Error: Cannot compile unknown node "some type"

I suspect the AST might rely on type + value internally, and might be making an exception for handling these when they exist on built in elements such as input, which works fine (<input type="some type" value="some value"></input>).

I'm wondering if theres a way to specify how to handle these existing on custom elements?

I saw something which I think is somewhat related on the remark-rehype package, but we're not using markdown (https://github.com/remarkjs/remark-rehype#unknown-nodes).

[ChristianMurphy]

Thanks for reaching out @Jamie452!
There may be an issue, but I don't think it is with the serializer.
Looking at https://codesandbox.io/p/sandbox/youthful-dream-znhyqc?file=%2Fsrc%2Findex.ts%3A15%2C30
The HTML AST (hast) can represent a type and value property without conflict, inside the properties object on the AST.
But the parser seems to be pulling the attributes in as children of the HTML element, instead of as properties.

It could either be a bug in the original parser https://github.com/inikulin/parse5 or in translator for parse5 to hast https://github.com/syntax-tree/hast-util-from-parse5
@Jamie452 would you be interested in digging in a bit more and tracing the root cause? Maybe opening a PR with a fix?