Comment by esprehn

Fwiw the XSLT implementation in Blink and WebKit is extremely inefficient. For example converting the entire document into a string, to parse it to a format that's compatible with libxslt, to then produce a string and parse it back into a node structure again. I suspect a user space library could be similarly as effective.

Ex. https://source.chromium.org/chromium/chromium/src/+/main:thi...

https://source.chromium.org/chromium/chromium/src/+/main:thi...

https://github.com/WebKit/WebKit/blob/65b2fb1c3c4d0e85ca3902...

Mozilla has an in-house implementation at least:

https://github.com/mozilla-firefox/firefox/tree/5f99d536df02...

It seems like the answer to the compat issue might be the MathML approach. An outside vendor would need to contribute an implementation to every browser. Possibly taking the very inefficient route since that's easy to port.