Support for grid tables with multiple table bodies

[tarleb]

This is a proposal to add support for multiple table bodies by treating two consecutive row separators as table body delimiter.

E.g., this table

+------+-------+
| Item | Price |
+======+=======+
| Eggs | 5£    |
+------+-------+
| Spam | 3£    |
+------+-------+
+------+-------+
| Sweets       |
+------+-------+
| Item | Price |
+======+=======+
| Ice  | 2£    |
+======+=======+
| Sum  | 9£    |
+======+=======+

would be parsed to

<table>
  <thead>
    <tr><th>Item</th><th>Price</th></tr>
  </thead>
  <tbody>
    <tr><td>Eggs</td><td>5£</td></tr>
    <tr><td>Spam</td><td>3£</td></tr>
  </tbody>
  <tbody>
    <tr><th colspan="2">Sweets</th></tr>
    <tr><th>Item</th><th>Price</th></tr>
    <tr><td>Ice</td><td>2£</td></tr>
  </tbody>
  <tfoot>
    <tr><td>Sum</td><td>10£</td></tr>
  </tfoot>
</table>

Note that the bodies can have header rows, but the first head separator (+===+) always marks the head of the full table.

[jgm]

I'm not sure. This does introduce an ambiguity, since currently

+------+-------+
| Spam | 3£    |
+------+-------+
+------+-------+
| Sweets       |
+------+-------+

is two distinct tables.

Also: I'm not clear about the significance of multiple table bodies. Can you give an example of a rendered table with multiple bodies, so I can see what it would be used for? (I know that HTML and our AST allow this.)

[tarleb]

Our test suite uses an example from MDN to test handling of multiple bodies. I don't particularly like these tables: most of the times those table should have an additional column instead, or be presented as separate tables. So I'm ok with not supporting them for now.

The updated parser follows rst interpretation of two consecutive row separators: it treats the above as a single table with three rows, where the second row is empty. I hadn't realize that we changed parsing behavior in this case.

[tarleb]

An image search for "rowgroup tables" yields a number of tables that, I have to admit, look like legitimate use cases for this feature. Example taken from this question.