how do i customize the the latex defined by myself, and change it to mathml defined by myself

Created by: jaylenchan

1. How can I convert my custom latex symbols to custom mathml

Cause: Now the server storage format is as follows: <?xml version="1.0" encoding="utf-8"?> <math xmlns="http://www.w3.org/1998/Math/MathML"> <mrow> <munderover> <mo>⇌</mo> <mi>A</mi> <mi>B</mi> </munderover> </mrow> </math>

but use mathjax convert \overset A{\underset B\leftrightharpoons}will get the result: <math xmlns="http://www.w3.org/1998/Math/MathML" display="block"> <mover> <munder> <mo stretchy="false">&#x21CB;</mo> <mi>B</mi> </munder> <mi>A</mi> </mover> </math>

the <munserover>will replaced by <mover> <munder>, I can't replace the store format, how can i do to solve this problem ?

in a word, i want to customize the mathml from input latex