If you want to find the 'pow' method, for example, and you don't know where it is, you might go to the method index (i.e. the a-z index underneath the search field in the left frame). You click on 'p' and then look for 'pow'. You won't find it - ScalaDoc doesn't put members of package objects into this index.
Another thing which I realized while browsing through the index is the way in which the index entries are written, i.e. are capitalized.
Example: STAR: is defined in Trees.Star, Base.Star and Tokens.STAR, but listed in the index as STAR only. Probably all defined capitalizations could be listed on the index-title-line instead of only one (arbitrarily) chosen one. (noticed by Dominik)