what is the point of the dst parameter of Insert ?

[chris-stones]

/// Inserts a list of rectangles into the bin.
/// @param dst The outputted list of rectangles. Note that the indices will not correspond to the input indices.
void Insert(std::vector &rects, std::vector &dst, bool merge,
FreeRectChoiceHeuristic rectChoice, GuillotineSplitHeuristic splitMethod);

From the code comment, I was expecting the function to write some results to it?
But looking at GuillotineBinPack.cpp, the variable is only ever referenced once, and thats is just a "dst.clear();"