public/javascript/libs/wysihtml5-0.3.0.js
function _addClass(element, className, classRegExp) {
    if (element.className) {
      _removeClass(element, classRegExp);
      element.className += " " + className;
    } else {
      element.className = className;
    }
  }
function _addClass(element, className, classRegExp) {
    if (element.className) {
      _removeClass(element, classRegExp);
      element.className += " " + className;
    } else {
      element.className = className;
    }
  }
Remove similiar classes (based on classRegExp)
and add the desired class name