This button removes the HTML formatting tags; abbr, acronym, address, b, big, blockquote, cite, code, del, em, font, i, kbd, pre, s, small, span, strike, strong, sub, sup, u.
It processes the selected text and replaces it with the format-free text.
js:
E.replaceSelection(E.getSelection().replace(new RegExp('</?(abbr|acronym|address|b|big|blockquote|cite|code|del|em|font|i|kbd|pre|s|small|span|strike|strong|sub|sup|u)(\\s[^>]*)?>', 'g'), ''));