The definition of the internal DirectX D3DVERTEX object is as follows:

struct D3DVERTEX {
union {
D3DVALUE x;
D3DVALUE dvX;
};
union {
D3DVALUE y;
D3DVALUE dvY;
};
D3DVALUE z;
D3DVALUE dvZ;
};
union {
D3DVALUE nx;
D3DVALUE dvNX;
};
union {
D3DVALUE ny;
D3DVALUE dvNY;
};
union {
D3DVALUE nz;
D3DVALUE dvNZ;
};
union {
D3DVALUE tu;
D3DVALUE dvTU;
};
union {
D3DVALUE tv;
D3DVALUE dvTV;
};
}