Handling of the "math" script tag

This is the current text at https://mathml-refresh.github.io/mathml-core/#opentype-features:

        <p>
          Good mathematical rendering requires use of non-Unicode glyphs.
          Mathematical fonts may only provide these glyphs when the
          <code>math</code> script tag is enabled [[OPEN-FONT-FORMAT]],
          so user agents must
          ensure that it is the case when rendering text inside the
          <code>&lt;mtext&gt;</code> element.
        </p>

From https://docs.microsoft.com/en-us/typography/opentype/spec/math:

         'math' | Script tag to be used for features in math layout. The only language  system supported with this tag is the default language system.

I believe this was only needed because of rtlm ( w3c/mathml#148 ) and ssty ( w3c/mathml-core#135 ). But we moved them to level-2 so it seems the same should be true for this.

Start with the opentype-features section in the MathML Core draft and compare its wording with the referenced OpenType specification. Read the linked rtlm and ssty issues to understand the move to level 2, then determine the corresponding treatment for the math script-tag requirement. Done means the specification text reflects the resolved level and remains consistent with those references.