I have never used such editor before and did not find how to change it to a HTML mode to enter code. Now I found the solution how to add a plain HTML code to the page:
{CODE(ishtml="1")}
put plain HTML code here
{CODE}
Inside works, problem is solved. What I do not like is that a {CODE} block has a dotted border and a different background. In my case it is not a problem, but can't be used as a generic formatting tool.
Thanks... Béla