I'm not asking without a real reason.

For sure it is all inside MUI documentation ... somewhere. And "somewhere"
is the problem. I read a lot of documents and yet did not find out about it. I
googled for example code and did not find it or did not recognise it. MUI documentation is
not very friendly to starters. It's like throwing someone into the hay and
saying "the needle is inside". So I am asking for a direct pointer please to
where to find it or a short example code and I'm asking for a real reason.