notifyModified called when object re-indexed

Can somebody explain why notifyModified is called from CatalogMultiplex
when re-indexing an object only if idxs is an empty list?

Here's the relevant code:

    def reindexObject(self, idxs=[]):
        if idxs == []:
            if hasattr(aq_base(self), 'notifyModified'):
                self.notifyModified()



-- 
Roché Compaan
Upfront Systems                 http://www.upfrontsystems.co.za