It is currently very hard to properly format anything in community post and comments. I found a couple posts mentioning markdown support but it doesn't seem to work at all currently.
A plain text editor with markdown is something that works and used by many great services out there (github, slack, vanilla forums, etc). It would really make Zendesk a great tool for communities if the editor was rock solid and efficient.
Markdown seem to be properly supported when creating a new ticket from the agent dashboard, including a must have preview mode; would be great to have the same thing for communities and even help center articles.