Massimo, I'm afraid the online web2py book search functionality is very ineffective- returning results as "Chapters Containing Matching Text" means you still have to drill into each chapter link to find what you're looking for. If you're searching for a common term, it basically gives you the entire chapter list, and you're no closer than when you started.
It would be much more helpful if search results were returned in totality, and with a snippet of the context. If they rolled up by chapter that would be nice, but that's secondary. I've spent a lot of time working through the online book this month, and the limited search capabilities have cost me a lot of time. Thanks, Yarin
