Since Resources 2.4 (Magnolia 5.4), the JCR-based resources app is deprecated.
Instead, the new resources-app lists all resources across classpath, file-system and the JCR 'resources' workspace.
@Deprecated
public class ResourceDropConstraint
extends BaseDropConstraint
Resource App specific implementation of info.magnolia.ui.workbench.tree.drop.DropConstraint.