The tbx:xMathML element is a hyperlinking element that points to an external location of a mathematical expression in MathML, for example:
<tbx:xMathML target="http://example.com/math/mathsample.html">Sample equation</xMathML>

The target attribute is required.

This element will be rendered in the published text with the label See: before it. The element content should contain the desired display text of the link.