code: func Register(name string, im Importer) {
  	if _, dup := importers[name]; dup {
  		panic("Dup registration of importer " + name)
  	}
  	if _, dup := reservedImporterKey[name]; dup {
  		panic("Dup registration of importer " + name)
  	}
  	if pt := im.Properties().PermanodeImporterType; pt != "" {
  		if _, dup := importers[pt]; dup {
  			panic("Dup registration of importer " + pt)
  		}
  		if _, dup := reservedImporterKey[pt]; dup {
  			panic("Dup registration of importer " + pt)
  		}
  		reservedImporterKey[pt] = true
  	}
  	importers[name] = im
  }
docs: // Register registers a site-specific importer. It should only be called from init,
  // and not from concurrent goroutines.