<fw> (convenciones gráficas.) contiene un encabezamiento, pie de página, reclamo o similar relativo a la página corriente [11.6 Headers, Footers, and Similar Matter]
Where running heads are consistent throughout a chapter or section, it is usually more convenient to relate them to the chapter or section, e.g. by use of the rend attribute. The fw element is intended for cases where the running head changes from page to page, or where details of page layout and the internal structure of the running heads are of paramount importance.