Extension:Math/annotation.js

/* Any JavaScript here will be loaded for all users on every page load. */  
/* Created by Amber Liu */
/* redfines semanticsAnnotations variable to add an additional annotation option to the menu */ 
mw.loader.using( 'ext.math.mathjax.localization', function () {
  MathJax.Hub.config.MathMenu.semanticsAnnotations= {
      "TeX": ["TeX", "LaTeX", "application/x-tex"],
      "StarMath": ["StarMath 5.0"],
      "Maple": ["Maple"],
      "ContentMathML": ["MathML-Content", "application/mathml-content+xml"],
      "OpenMath": ["OpenMath"],
      "/* what you want the menu button to say */" : ["/* tag that identifies your annotation */"],
    }  
} );