The object reactor creation example in About Using Object Reactors (AutoLISP) included a string, “Circle Reactor,” in the call to vlr-object-reactor. You do not have to specify any data to be included with the reactor; you can specify nil instead. However, an object may have several reactors attached to it. Include an identifying text string, or other data your application can use, to allow you to distinguish among the different reactors attached to an object.