  We present a decomposition principle for general regular Dirichlet forms
satisfying a spatial local compactness condition. We use the decomposition
principle to derive a Persson type theorem for the corresponding Dirichlet
forms. In particular our setting covers Laplace-Beltrami operators on
Riemannian manifolds, and Dirichlet forms associated to $\alpha$-stable
processes in Euclidean space.
