Expose xmodule_runtime as .runtime if it's set (otherwise, fall back to the supplied runtime). This causes all blocks to act like XModules when they have a ModuleSystem, and like XModuleDescriptors if they only have a DescriptorSystem.
Expose xmodule_runtime as .runtime if it's set (otherwise, fall back to the supplied runtime). This causes all blocks to act like XModules when they have a ModuleSystem, and like XModuleDescriptors if they only have a DescriptorSystem.