code: function(element, className) {
      invariant(
        !/\s/.test(className),
        'CSSCore.removeClass takes only a single class name. "%s" contains ' +
        'multiple classes.', className
      );
  
      if (className) {
        if (element.classList) {
          element.classList.remove(className);
        } else if (CSSCore.hasClass(element, className)) {
          element.className = element.className
            .replace(new RegExp('(^|\\s)' + className + '(?:\\s|$)', 'g'), '$1')
            .replace(/\s+/g, ' ') // multiple spaces to one
            .replace(/^\s*|\s*$/g, ''); // trim the ends
        }
      }
      return element;
    }
docs: Removes the class passed in from the element
  
  @param {DOMElement} element the element to set the class on
  @param {string} className the CSS className
  @return {DOMElement} the element passed in