I always think of a line/pipe block as a container for rows, i.e. a one-column table which is (perhaps optionally) realized with different (simpler) markup, i.e. <br>
instead of <tr>
etc.
| What is | this?
A headerless single-row two-column table, accordingly.
<table><tbody>
<tr><td> What is </td><td> this? </td></tr>
</tbody></table>
| 1. This is a | list with a line break
This could also become a two-row table.
<table><tbody>
<tr><td><ol><li> This is a </li></ol></td></tr>
<tr><td> list with a line break </td></tr>
</tbody></table>