We further restrict discussion to continuous Hermite finite elements which have at least first-derivative degrees-of-freedom. With this, one can draw a large number of candidate triangular and rectangular elements from the plate-bending literature. These elements have derivatives as components of the gradient. In 2D, the gradient and curl of a scalar are clearly orthogonal, given by the expressions, ∇ ∇ φ φ = ( ∂ ∂ φ φ ∂ ∂ x , ∂ ∂ φ φ ∂ ∂ y ) T , ∇ ∇ × × φ φ = ( ∂ ∂ φ φ ∂ ∂ y , − − ∂ ∂ φ φ ∂ ∂ x ) T .