[AlanHK]

I thought I was clever when I worked out how to add pseudo-kerning between a single and double quotemarks, so they didn't turn into a triple.

I noticed some books put a normal space, [“ ‘]
but that allows a linebreak between the quotes. I thought   looked too wide, so I use : [“ ‘].

And later when indenting some poetry, I used   (em-space) characters.

That looked okay on Sigil. And I'm told it works on iPad iBooks.

But I noticed both these characters display as black boxes in Calibre's ebook-reader.

Is that just a bug in Calibre, or are these characters not officially meant to be used in ePubs?