pub type LengthOrNumber = GenericLengthOrNumber<Length, Number>;
Either a <length> or a <number>.
<length>
<number>
enum LengthOrNumber { Number(Number), Length(Length), }
A number.
NOTE: Numbers need to be before lengths, in order to parse them first, since 0 should be a number, not the 0px length.
0
0px
A length.