It binds TAB to ruby-indent-line. That is against the rules. ;-)
Out of curiosity, are 'rules' like this codified anywhere?
Not much, sadly. There Elisp manual has a section about coventions to
follow for major modes, so the info should be there, but there's a lot
more conventions than the documented ones.
But as a general rule, if you want key K to do something it's preferable
to do it by setting some variables that affect K's default binding than
by rebinding it to another command.
I.e. better set indent-line-function, fill-paragraph-function,
completion-at-point-functions, rather than rebing TAB, M-q , M-TAB, ...
The general goal should be to make it easier for a user to state
global preferences that affect all modes.
As I've started using Emacs seriously again, I've started noticing
a lot of little inconsistencies between extensions (e.g., how
temporary windows are displayed/destroyed). I'd be happy to submit
patches to help improve this if someone could point out the
correct behavior.
These are usually welcome here (although they also tend to be delicate
because users get quickly used to the old behavior and then show
resistance to change).
Stefan