Why does OpenCV not define the alias Size2d?

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For convenience, the following type aliases are defined in OpenCV:

typedef Point_<int> Point2i;
typedef Point2i Point;
typedef Point_<float> Point2f;
typedef Point_<double> Point2d;
typedef Size_<int> Size2i;
typedef Size2i Size;
typedef Size_<float> Size2f;

Why does OpenCV not define the alias Size2d for Size_<double>?