A row in the table grid. The list of cells it maintains is always large enough to set a table cell at every position in the row. If there are no colspans, rowspans, or missing cells, the grid row will exactly correspond to the row in the original markup. On the other hand, colspans may force spanning cells to be inserted, rowspans will mean cells appear in more than one grid row, and positions may be null if no cell occupies that position in the grid.