Add v to the end of the array. v is no longer valid after the append
Return 0 if the value is false, 1 if it is true, and 2 if it is not a bool.
Return 1 if the value is null, else 0.
If the value is a number, return 1 and store the number in out, otherwise return 0.
If the value is a string, return it as UTF8 otherwise return NULL.
Add the field f to the object, bound to v.