Re: [css-transforms] 'transform-box' defaults in svg

On Wed, Sep 30, 2015 at 8:31 AM, Amelia Bellamy-Royds
<amelia.bellamy.royds@gmail.com> wrote:
> Erik: Are you suggesting that the `auto` value would use the viewBox as the
> reference if `transform-origin` was set in absolute units, and `fill-box` as
> a reference if it used percentages?
>
> That sounds very difficult to implement & unnecessarily confusing.  What if
> the `transform-origin` included calc() functions?  Or was animated between
> different values?  An animation between 100px and 100% is implemented as an
> animation between `calc(100px + 0%)` and `calc(0px + 100%)`.

Yes, it's unofficially illegal (at the spec design level) for
percentages to resolve differently than absolute lengths, for
precisely the calc() issue you bring up.  It makes % and px no longer
comparable units, and requires us to have special spec prose defining
how to combine them in a calc().  Some legacy values (like <position>)
have that, but we're not adding it to anything else.

~TJ