1. 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)
2. If there's no index page for letter 'X', the link is still valid and will lead to a 404 error because no page was generated.