I was trying to work how how to do blockquotes myself last week, when I thought I needed them for a post. The standard markdown for a blockquote is a < symbol but that sdoesn't have any effect here.
I am trying your "four spaces" version now to see how that works. I need to type another sentence or two to make sure I have a blockquote that is more than one line.
That should do it!
So, if this works, I should now have two paragraphs in blockquotes :) Oops: the Ello smiley is only supposed to be )
Seconds later, in edit mode... ah, I see. It creates a nice grey quote box. Many thanks. That is nice and useful. And it led me to follow @booksnips too, because anyone who is worrying about block quotes is my kind of person.