This was added in Level 2 of the Web Animations spec
In this level of the spec, all time values associated with animations
(including this duration property) are no longer simple numbers but are
instead either percentages or numbers for progress- and time-based
timelines respectively. These values are represented internally by a new
`TimeValue` wrapper struct, and externally (i.e. in JS) as
`CSSNumberish`.
Because we store calculations as a tree of CalculationNodes inside a
CalculatedStyleValue, instead of a tree of StyleValues directly, this
implements a create_calculation_node() method on CSSNumericValue.
CSSMathValue::create_an_internal_representation() then calls
create_calculation_node() on itself, and wraps it in a
CalculatedStyleValue.
Lots of WPT passes again! Some regressions, which are expected: `cursor`
fails a test for the same reason it fails other that set it to some
kind of numeric value: We don't distinguish between "can contain a
number" and "can accept a number by itself". This will affect any
similar properties, but overall this is a big improvement.
DOMMatrix.to_string() throws exceptions if any of its values are
non-finite. This ends up affecting CSSStyleValue because its subclass
CSSTransformValue (which is about to be added) serializes
CSSTransformComponents, and one of those is CSSMatrixComponent, which
calls DOMMatrix.to_string().
This is all quite unfortunate, and because at the time the spec for
DOMMatrix was written, CSS couldn't represent NaN or infinity. That's
no longer true, so I'm hoping the spec can be updated and this can be
reverted. https://github.com/w3c/fxtf-drafts/issues/611
What I thought was a spec issue was actually a combination of my own
misunderstanding and a bug in our IDL generator. With that bug fixed, I
can correct this to how it is in the spec.
Reifying the result gets quite ad-hoc. Firstly because "parse a
component value" produces a ComponentValue, not a full StyleValue like
we need for math functions. And second, because not all math functions
can be reified as a CSSNumericValue:
Besides the fact that I haven't implemented CalculatedStyleValue
reification at all yet, there are a lot of math functions with no
corresponding CSSMathValue in the spec yet. If the calculation tree
contains any of those, the best we can do is reify as a CSSStyleValue,
and that isn't a valid return value from CSSNumericValue.parse(). So, I
made us throw a SyntaxError in those cases. This seems to match
Chrome's behaviour. Spec issue:
https://github.com/w3c/css-houdini-drafts/issues/1090
