As requested in the parent ticket by dobedobedoh's peer review, this subtask was split to focus onto the necessary changes to blockquote editing in atto.

Our original idea was:

• The Atto plugin will have to handle the styling of the quote and the management of replies which are inserted into the quote like it's possible with every today's email client (handling cases like to split the div at the point when the 'enter' key was pressed, adding a non-styled section in between).
• Based on that functionality, it would make sense if the Atto plugin can also be used detached from the use case at hand as a quote-styling button (especially as MDL-48905 and MDL-45662 to implement blockquotes in Atto seem not to come to an end).

Andrew answered this in his peer review:

We should really use the standard HTML blockquote when creating the quoted text, so I don't know exactly what changes would be made in Atto and I think this is likely to be the area of most critique in this issue. You'd need to go into a bit more detail on how you'd anticipate this working, especially for those adding multi-line block quotes. I guess you're looking for something like Jira when dealing with markdown - e.g. if you are in a list, and press return, you continue in the last. If you press return again, it exits the list.

I would agree that we can use the blockquote tag instead of a custom div for the quote paragraphs. And you are completely right that this part needs some more elaboration.

However, we can already say that there are some basic things which will have to be changed to have Atto "officially" support blockquotes:

• A user should be able to set an existing paragraph as quote (see especially MDL-45662 which is blocked by MDL-48905 and where nothing has happened since ages) in all Atto instances, independently from Atto inside forums.
• Moodle as a whole and the Atto preview has to display a blockquote tag as quote (currently blockquotes are simply not distinguishable from normal paragraphs)
• Atto has to support multiline blockquotes in a way like users expect it from today's mail systems and especially in a way to let the user split a blockquote easily into to parts and insert a normal paragraph in between.