"The maximum distance between the top of the cell box and the baseline over all cells that have 'vertical-align: baseline' is used to set the baseline of the row. If a row doesn’t have any cell that has 'vertical-align: baseline', the baseline of that row is the bottom content edge of the lowest cell in the row.

The baseline of a table-root is the baseline of its first row, if any. Otherwise, it is the bottom content edge of the table-root."

This definition for first baseline is good! - We also need to define the last baseline behaviour.

Something like:
"The last baseline is defined as:

• The maxiumum distance between the top of the cell box and the last baseline over all the non-rowspanned cells that have 'vertical-align: baseline' is used to set the baseline of the row.
• If the row doesn't have any non-rowspanned cell that has 'vertical-align: basleine', the baseline of that row is the bottom content edge of the lowest cell in the row.

The last baseline of a table-root is the baseline of its last row, if any."

Ian