I am a little late at the party, but, as the tests have been made, I congratulate Ruben too for his inventive proposal. The "pre" property should be recognized by any user agent.
As far as I am being concerned, I'll be sticking with the
nbsp first solution because this no-break space is quite commonly used for French books.
Users of KFX format may make other choices. Each one its own...
P.S. Mobi, someone said "Mobi"? What's that?
