In a previous question I used the "#" header for the first time to create a tabbed post. But as soon as I posted it to the site I noticed that the block quotes encroached upon the tabs, and that the tabs, hiding behind the block quotes, were difficult to click on. Chocolate's edit solved it by adding two characters, one after each header. They appear to be simple spaces, but as I am writing a new post using headers, I can't seem to get it to work the same way with spaces. So what exactly did the trick in Chocolate's edit?
Chocolate's edit inserted a
U+200A HAIR SPACE.
I'm not tech savvy enough to tell you exactly why it's happening, but it appears that the language tabs don't work well when the first line is a quote.
As a rule of thumb, only spaces are ignored in HTML, so when you insert some other kind of white space, it treats it as a proper character (without displaying anything of course), making the first character a hair space and not interfering with the quote markup.