As MathLib.js is a JavaScript Library, the demos will only work if you have JavaScript enabled. If you need help enabling JavaScript, please have a look at these explanations.
This demo shows MathLib's ability to parse content MathML. The Content MathML is converted to MathLib's internal format and then to presentation MathML to display the math on the page. You can edit the MathML. To apply the changes click somewhere on the page.