* If neither is specified, the <<.field list>> field is used by default. So `[list[T]]` outputs the titles listed in the <<.field list>> field of tiddler T.
* If <<.place R>> consists of <<.em only>> a field or a property, the tiddler part of the reference defaults to the [[current tiddler|Current Tiddler]]. So `[list[!!tags]]` outputs the titles listed in the <<.field tags>> field of the current tiddler.