@DavidCarlisle Ah, I think I have to read
en.wikipedia.org/wiki/MathML to get some knowledge about it. I just need math for some articles I write. This was the reason why I asked a MathJax developer once if mathjax would be less heavy (processing time and download time) if MathML would be supported by all browsers. The answer was "yes". So I assumend that browsers do not support MathML properly.