Use escaped space as  

Spec
19

I like this idea of seeing a table in both uses: it is always good to eliminate special syntax for special cases.

I have written a proposal to extend the CommonMark specification to include tables which would render both your examples in the way as intended (well, I hope the rules do have this effect, and that the following is the intended table structure in each example):

  1. The first one as a single-row, two-column table without a table header, as shown;

  2. the second one as a single-row, single-column table with an ordered list in it’s (sole) table data cell; and this list contains one item with a <br> after this is.

So the second example should produce “what it says in the content” :wink: :

<table><tbody>
  <tr><td><ol><li>This is a<br>list with a line break</li><ol></td></tr>
</tbody></table>

You’re welcome to take a look, and feel free to comment or suggest improvements:

http://talk.commonmark.org/t/rfc-spec-extension-for-tables-syntax-and-transformation-rules/1910/1