Date Markers - Default behavior is to mark the currently selected date and not today, but this can be customized to suit your needs. If both are marked and coincide on the same day, it will show up with the current selection color, not today's color. Headers - Default behavior is to show the headers, but they can also be hidden, in which case everything else will get shifted up accordingly (after a set needs display call). Preferred Week Start - Default behavior behavior is Monday. Determines what day of the week is in the leftmost column. It's very simple and useful to create calendar base on your locale and of course your country.