MathML - slide "Mixing Content and Presentation Markups"

Mixing content into presentation markup helps accessibility issues (eg, voice reader); but ...
content markup cannot account for all situations (missing function names or constructions, notational differences among countries, disciplines)! For example:

  <apply>
    <mrow>
      <msub>
        <mi>F</mi>
        <mi>i</mi>
      </msub>
    </mrow>
    <ci>x</ci>
  </apply>