The very bad user experience of the LilyPond manual, ie. very-very bad
navigation was the very cause I started LilyPondTool 5 years ago
(http://lists.gnu.org/archive/html/lilypond-user/2003-09/msg00561.html).
Because I was as confused as you.
Then the quite hard content of the documentation regarding to tweaks
made me develop the autocompletion, because I was confused about
\override and \set and grobs (what the hell is a grob) so on.