@akhleung is working on hcatlin/libsass and was wondering how
implemented in the Ruby implementation of Sass. Rather than just tell him, I
thought I'd write up a public document about it so anyone who's porting Sass or
is just curious about how it works can see.
Note that this explanation is simplified in numerous ways. It's intended to
explain the most complex parts of a basic correct
@extend transformation, but
it leaves out numerous details that will be important if full Sass compatibility