My reasoning for this is that "transform" is a heavily overloaded word, just like "coordinate system".  So I'm trying to use "transform" to mean "change from one reference system/frame to another", but *not* for transforming representations.  It's mostly semantics, but the discussion around this had a lot of confused/overlapping terminology, so I'm trying to push this API in the direction of being rather pedantic.

Other opinions on this? @mdboom @astrofrog @Cadair ?