In the algorithm for serializing CSSMathValue, it repeatedly ends up calling "serialzie a CSSNumericValue", because that's what CSSNumericArray contains. eg:

2. If this is a CSSMathMin or CSSMathMax:
3. Append "min(" or "max(" to s, as appropriate.
4. For each arg in this’s values internal slot, serialize arg with nested and paren-less both true, and append the result to s, appending a ", " between successive values.
5. Append ")" to s and return s.

However, serialize a CSSNumericValue doesn't make use of those arguments. It only accepts the minimum/maximum arguments that are relevant for CSSUnitValue. It needs to take the nested and paren-less arguments, and then pass them to "serialize a CSSMathValue".