How to describe this expression via MathML?

Question

I'm developing interactive education application, which should works on modern smartphones, tablets and on PC. Our target platforms are iOS, Android and Windows. Program also as Its content are created within our company. Content is a set of books that contains a lot of mathematical expressions and formulas.

The books are created in XML-form (semantic representation) and then translated into html using our conversion program based on XSLT transforms. For describing mathematical expressions I'm going to use MathML. I'm going to use MathJax library directly on the client device for rendering MathML expressions.

But I have detected the strange expressions in the books.

They look like this.

I'm stuck with the questions how we can describe those expression via MathML and then render it properly within HTML-document. I don't know how to make the fraction with doubled-lines.

I'm not a guru in MathML and HTML, CSS. I suppose that there is a simple solution.

Answer 1

How about

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <munderover>
    <mo stretchy="true">=</mo>
    <mi>a</mi>
    <mi>A</mi>
  </munderover>
</math>

This should put the "A" over a stretchy equal sign and the "a" under it.