See documentation for the HTML 4.0 (XHTML) table model.
The number of rows a cell spans, in other words, a vertical span (The table cell content will be tagged with a <td> or <th> element.)
| Value | Meaning |
|---|---|
| A counting number | How many rows this cell will span vertically, e.g., “3” |
| Default value: 1 (Span 1 row) | |