Darn, should be "previous".proper TR14 line breaking needs a precious character LB property and a whitespace status
I'm not sure what you're referring to here--the TR at http://www.unicode.org/unicode/reports/tr14/, doesn't appear to mention a "whitepace status" or LB "property" per se.
In order to determine whether a line break can be inserted between two non-space characters with optional space chars in between (which would either be left at the end of the line or discarded), the algorithm needs the LB properties of both the characters as well as whether any space was encountered. The line breaking property (those "AL" etc. stuff) is defined in one of the Unicode data files for each character.
Hmmm...not that big a deal to me, but I would be inclined to keep the whitespace removal out of the LayoutManagers, because it is fo:block specific
I don't quite understand this argument. Handling space-before is also fo:block specific. Where should this logic be put, then? Note that whitespace handling includes removing spaces around line breaks which are introduced during the layout process.