CSS styling for devanagri scripts

I was just curious about the language specific features for the open-type
fonts, while reading the W3C-CSS convention Section 3. What I could not get
is how can we really alter and control them? For example if I take the
devanagri script then are there styling properties which are specific only
to Devanagri script? If yes, then could someone please brief me about it ?
Also the rendering of the font-features might be following some particular
method, which could be translated as modification of glyphs using
font-developing applications ? If yes can someone please tell me, what are
the methods used for rendering so that I can replicate it some where ?