built-in data type
 The markup events of markup-element-event type represent element events that trigger an element rule when encountered by do markup-parse in a markup source. This event type is
        a subtype of markup-region-event, which means that it is signalled using #markup-start and #markup-end.
      
 You can obtain a markup-element-event instance in following ways:
        
#current-markup-event inside an element rule,
          
current elements shelf during a parse, or more generally from the elements of shelf,
          
create-element-event.
        
 Given one markup-element-event instance, you can access other element events related to it using
        various element expressions:
        
 Every markup-element-event has the following properties associated with it, either from its
        declaration or assigned by the parser: