[css-typed-om] prose description of CSSNumericValue.toSum() should explain empty units behavior

[dbaron]

The definition of CSSNumericValue.toSum() has an algorithm that treats an empty list of units as allowing all units rather than allowing no units. However, the prose description prior to the algorithm doesn't mention this. It should, so that readers who don't go through the whole algorithm will be aware of it.

[dbaron]

Er, ignore me. It does say this. It's just after a parenthetical...