PaymentRequest type checks (valid non-negative monetary value)

[marcoscaceres]

The following should be combined:

If details.total.amount.value is not a valid decimal monetary value, then throw a TypeError.
If the first character of details.total.amount.value is U+002D HYPHEN-MINUS, then throw a TypeError. total must be a non-negative amount.

We should just define a "valid non-negative monetary value" as an algorithm that calls into "valid decimal monetary value".

[marcoscaceres]

(updated the above)

[halindrome]

I don't mind this. However, if we do this we need to ensure that the relevant prose is preserved. We often (in specs) err on the side of a well expressed algorithm at the expense of its readability by mere mortals.

[zkoch]

@marcoscaceres is this something we want for CR?

[marcoscaceres]

The spec if fine as is.