Key Ref Positions of function Price in Tradable refers to an optional integer that defines the position within the array - if any - associated with the given key of the parameter that is being set to a specific number before the evaluation takes place.
If more than one objects are specified in Ref Objects, then an array of corresponding integers is expected here.
The entries here correspond to those in
This means that if an array of keys is supplied in Ref Keys, a similar array of integers must be supplied here.
Then the first row of integers will correspond to the first row of keys in Ref Keys, the second row of integers will correspond to the second row of keys and so on.
More details about the meaning of each integer are available at