Abstract supertype for all (static schema) capabilities. It is in fact just a shortcut
to introduce common "enabled" flag. As custom capabilities are expected to be in a
dynamic schema this has probably very little conceptual value.
Element specifying whether the capability is enabled or disabled.
Enabled capability work as usual (this is the default). Disabled capability
acts as it is not there at all. This is used to disable undesirable
native capabilities.
Each capability definition should have this element. It is made a top-level
element in this XSD definition to make that easier.