Use escaped space as  

Spec
18

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>