Problem and impact

We're using marked.js to render Markdown previews. However, marked.js can only support all of or none of GitHub flavoured Markdown. Our Python implementation, however, isn't GHF, but still supports line breaks (via the nl2br extension). Marked.js has to turn on full GitHub compatibility to support line breaks, which will also e.g. turn on lists working without an empty line beforehand.

Expected behaviour

Preview and actual rendering work the same.

Steps to reproduce

Test text:

This should
display as a line break

but this should
- never be a list

Other inconsistencies

• The frontend renderer also supports strikethroughs, whereas the backend renderer doesn't. Fixed by 98448c1
• The frontend and backend renderer disagree on how indented/nested unordered lists work, ie. how much whitespace is needed to trigger the indent. The failure case (very obnoxious) is that the frontend renderer shows an indented list, but the backend renderer outputs a list with all bullet point on the same level. This is because the JavaScript renderer accepts two (or any?) indent for nesting, while the Python renderer requires four spaces. I am on the side of the frontend here, honestly, and we may copy or depend on mdx_truly_sane_lists to fix this.