To be honest this isn't that strange, the parser needs to know what denomination you're trying to subtract.. Also as per the spec the `-` operand requires a whitespace. So it's not actually valid to use (100& -0) you're getting a false positive..
Example is you can * no problem, its expecting only a number for the 'read_next' but with the `-' it's expecting a denomination, otherwise it needs to keep a 'state' as such when moving on from reading a `0`
Edit : as pointed out by zarzavat : it does seem to be a bug in the spec in this case.
Pretty much what we're saying. It also fails when typed directly, at least in Firefox (as unnecessary as that 0 is).
While that might be true for all the length units defined in CSS, it's not true in general. E.g. in temperature, 0F != 0C
Thanks, my bad. I fixed the title.