Make PDF ticket output subevent-compatible

src/pretix/base/ticketoutput.py

@@ -45,6 +45,13 @@ class BaseTicketOutput:
         This method should generate the download file and return a tuple consisting of a
         filename, a file type and file content. The extension will be taken from the filename
         which is otherwise ignored.
+
+        .. note:: If the event uses the event series feature (internally called subevents)
+                  and your generated ticket contains information like the event name or date,
+                  you probably want to display the properties of the subevent. A common pattern
+                  to do this would be a declaration ``ev = position.subevent or position.order.event``
+                  and then access properties that are present on both classes like ``ev.name`` or
+                  ``ev.date_from``.
         """
         raise NotImplementedError()