Manually forcing line breaks?

Good evening,

Please excuse me if I'm not on the right mailing list. 

In my document, at different levels (chapter, sect1), I have sometimes very 
long lines as titles. The docbook xsl-fo stylesheet break these lines, but 
don't follow the rules of a «nice» french typography (articles like «le», 
«la», «les» shouldn't stay at the end of a line, but should be pushed at the 
beginning of the following line - of course only for the PDF output, it 
doesn't matter for the HTML output).

In the final version of my document, I'm ready to take a few time to have a 
«nicer» result.

Is there a way to force line breaks in my docbook source document? I can't find 
anything about this topic in the documentation.

Philippe Faehndrich