Unicode support for XML and HTML tags name #196

Tempest version

3.0

PHP version

8.5

Operating system

macOS

Description

Currently, for XML and HTML, we are capturing at best \w which translate into [a-zA-Z0-9_]. But tag names can contains almost any unicode characters after the first char (this one must be [a-zA-Z] for HTML, a bit more permissive for XML).

Here's the specs I've found for each language:

• XML: https://www.w3.org/TR/REC-xml/#NT-NameStartChar
• HTML: https://dom.spec.whatwg.org/#valid-element-local-name

The HTML spec even gave us a valid ReGex: /^(?:[A-Za-z][^\0\t\n\f\r\u0020/>]*|[:_\u0080-\u{10FFFF}][A-Za-z0-9-.:_\u0080-\u{10FFFF}]*)$/u

So the following are valid in HTML:

<math-α></math-α>
<emotion-😍-emoji></emotion-😍-emoji>

(And I guess even GitHub doesn't render then correctly 🥲)

Here's how Gecko (Firefox) is rendering the above HTML: