I like to replace ellipses with spaced periods, since I don't like the usual ellipsis glyph, and it doesn't allow variations like . . . . or . . . ? or . . . !
Also to space between nested quotemarks, which otherwise look like a triple mark ’” but with space ’ ”.
I see some books just use a normal space, but that allows a linewrap to occur, which should never be.
So I have been using
Aside from being no-break, otherwise it acts the same as a normal space; and so it stretches or compresses when the text is justified, and that sometimes looks odd.
I just looked at a Random House epub that used thin spaces:  
Which looks better I think. However, is it treated as a no-break space, in all formats -- epub and Kindle?
While looking into this, I found this list of 17 Unicode space characters:
http://www.fileformat.info/info/unic...ry/Zs/list.htm
U+0020 SPACE
U+00A0 NO-BREAK SPACE
U+1680 OGHAM SPACE MARK
U+2000 EN QUAD
U+2001 EM QUAD
U+2002 EN SPACE
U+2003 EM SPACE
U+2004 THREE-PER-EM SPACE
U+2005 FOUR-PER-EM SPACE
U+2006 SIX-PER-EM SPACE
U+2007 FIGURE SPACE
U+2008 PUNCTUATION SPACE
U+2009 THIN SPACE
U+200A HAIR SPACE
U+202F NARROW NO-BREAK SPACE
U+205F MEDIUM MATHEMATICAL SPACE
U+3000 IDEOGRAPHIC SPACE
Are all these valid in ebooks?
I assume that only the first two are elastic in size, is that correct?
And aside from nbsp, which are no-break?
Apologies if this is a FAQ, please link if there is such.