function setClasses(classes) {
    var className = docElement.className;
    var classPrefix = Modernizr._config.classPrefix || '';

    if (isSVG) {
      className = className.baseVal;
    }

    // Change `no-js` to `js` (independently of the `enableClasses` option)
    // Handle classPrefix on this too
    if (Modernizr._config.enableJSClass) {
      var reJS = new RegExp('(^|\\s)' + classPrefix + 'no-js(\\s|$)');
      className = className.replace(reJS, '$1' + classPrefix + 'js$2');
    }

    if (Modernizr._config.enableClasses) {
      // Add the new classes
      className += ' ' + classPrefix + classes.join(' ' + classPrefix);
      if (isSVG) {
        docElement.className.baseVal = className;
      } else {
        docElement.className = className;
      }
    }

  }
setClasses takes an array of class names and adds them to the root element

@access private
@function setClasses
@param {string[]} classes - Array of class names