1. A method of managing permissions, comprising: receiving at a processor a hierarchical document permission model, the hierarchical document permission model describing a document hierarchy comprising a plurality of document nodes that are hierarchically related, defining for each of at least a subset of said plurality of document nodes one or more document roles, and defining for each such document role of the one or more document roles one or more document permissions with respect to that document node, wherein the hierarchical document permission model associates the one or more document permissions with respect to that document node with a condition comprising a specified state; and using by the processor the hierarchical document permission model to determine and enforce permissions with respect to case management instances to which the hierarchical document permission model applies, wherein using the hierarchical document permission model includes adjusting the one or more document permissions associated with respect to that document node in response to a change associated with the specified state of that document node of the plurality of hierarchically related document nodes, wherein using the hierarchical document permission model to determine and enforce permissions with respect to case management instances to which the hierarchical document permission model applies comprises: receiving a request to perform an action with respect to a document associated with a case management instance, wherein the document is associated with the hierarchical document permission model and the request affects a portion of the document associated with an affected document node of the document hierarchy; determining that a requesting user associated with the request is assigned an assigned document role with respect to the case management instance; determining that the assigned document role is granted in the hierarchical document permission model, with respect to the affected document node, a permission required to perform the action with respect to the document node; and allowing the action to be performed based at least in part on the determination that the requesting user is associated with the assigned document role and the determination that the assigned document role is granted in the hierarchical document permission model the permission required to perform the action with respect to the document node.