[Zope] BTrees

Hi, I've seen here and there many references to IIBTrees and OOBTrees... Can anybody say me : - what are these classes used for ? In which context should they be used ? - is there any help and/or doc about them ? - anything to know about...?? Thanks for any help, Thierry -- Linux every day, keeps Dr Watson away... http://gpc.sourceforge.net -- http://www.ulthar.net