docs: def compile_loaderplugin_entry(self, spec, entry):
          """
          Generic loader plugin entry handler.
  
          The default implementation assumes that everything up to the
          first '!' symbol resolves to some known loader plugin within
          the registry.
  
          The registry instance responsible for the resolution of the
          loader plugin handlers must be available in the spec under
          CALMJS_LOADERPLUGIN_REGISTRY
          """
  
          modname, source, target, modpath = entry
          handler = spec[CALMJS_LOADERPLUGIN_REGISTRY].get(modname)
          if handler:
              return handler(self, spec, modname, source, target, modpath)
          logger.warning(
              "no loaderplugin handler found for plugin entry '%s'", modname)
          return {}, {}, []