code: public static String openTagClass(String tag, String clazz, String... content) {
  		return openTag(tag, clazz, null, content);
  	}
docs: Build a String containing a HTML opening tag with given CSS class and concatenates the given content.
  Content should contain no HTML, because it is prepared with {@link #htmlEncode(String)}.
  
  @param tag String name of HTML tag
  @param clazz CSS class of the tag
  @param content content string
  @return HTML tag element as string