To get strikethrough I have to go to plain text and use double tilde markdown: ~~ABC~~. However, if I switch back to the rich text editor the tildes are escaped as \~\~ABC\~\~, and I have to go back to the plain text editor, remove the back slashes, and post from there.

I need a strikethrough button on the rich text editor, and it should not escape the markdown from the plain text editor.

(This is important, because I want students who put up a wrong answer not to take it down, so others can learn from the comments on it. Instead, they are instructed to edit, strikeout the incorrect portions, and correct them. Changing font color would be an alternative, if that were available in the editor.)