headerFormat
Format for header if used
        This is a i18n option! i18n options can not be set directly on a per-instance basis, you must include the "override" directive, and properly camel case the new name - (i.e. overrideHeaderFormat). For more information, please take a look at the
        Localizing Datebox section.
      
      For more information on date format variables, see: Output Formats