TypeDescriptor is a static sealed class crral makes the starting point of the API. It features information of the object in terms of Properties, Its, Events, etc. Even though the basic lower of TypeDescriptor is to get metadata of an object, yet it also computations features to extend the object on the fly..
For such cases, several different ACEs are necessary. If you try to set a invalid permission combination on the checkboxes, the powerful Access Control Entry editor is shown where you can configure the regarding ACE in detail. Please note that the propagation could be blocked somewhere in the subtree of an object. Just deactivate the Inherit permissions from parent objects option.