The structure of 'VectorL2()' in the cpp document

Hi,

In DG methods, we set a quadrilateral mesh like this:

mesh = ngm.MakeStructured2DMesh(quads=True, nx=10, ny=10)
V = VectorL2(mesh, order=3, dgjumps=True)

In fact, we want to add some vector basis to the vector space V. So it is essential to know how the vector basis is composited in V. I guess it hides in one core documents but cannot find it.

Best,
Di Yang

PS:
For example, like BDM element in a rectangle, one adds two vector basis ( -x**{k+1}, (k+1)x**ky ) and ( (k+1)xyk, -y{k+1} ) to the standard PkPk.
Now, we want to add ( -x**{k+1}, (k+1)x**ky ) and ( (k+1)xyk, -y{k+1} ) to Qk
Qk element-by-element in a quadrilateral mesh. How can we finish it ? I know it is a tricky work.