[css4-images] Comments on cross-fade

- I think it would make sense to make the <percentage> in cross-fade() [1] optional, with a default value of 50%. Otherwise, I anticipate it will break many author expectations.
- Why not allow any order? There doesn’t seem to be a disambiguation reason to mandate that the percentage goes first, but I might be missing something.
- Not sure about this, but why not allow multiple arguments? Sure, one can nest multiple cross-fade() calls, but it starts looking like Lisp :-) Not sure how frequently that is needed, but it doesn’t seem much extra effort for editors or implementors, so why not?

[1]: http://dev.w3.org/csswg/css4-images/#cross-fade-function


Lea Verou
W3C developer relations
http://w3.org/people/all#lea ✿ http://lea.verou.me ✿ @leaverou