The function withMathJax() is a wrapper function to load the MathJax library in a shiny app. For static HTML content, we only need to call withMathJax() once. However, for dynamic UI output via renderUI(), we must wrap the content that contains math expressions in withMathJax(), because we have to call the MathJax function MathJax.Hub.Queue(["Typeset", MathJax.Hub]) to render math manually, which is what withMathJax() does.