See W3C documentation for the XHTML table model.
The footer rows and columns within a standard XHTML table.
<tfoot> holds table metadata just as the table header rows do, for those tables that have metadata at both the head and the foot. The footer is defined separately from the body of a table so that table processing software can treat it differently, for example making the table footer bold or repeating the footer when a table breaks across pages.
(tr)+
<tr> Table Row (XHTML table model), one or more
xhtml-table-1.mod