((p "With a " (a (@ (href . "00001007710000")) "list of zettel identifier") ", a " (a (@ (href . "00001007720000")) "query directives") ", or a " (a (@ (href . "00001007701000")) "search expression") ", a list of zettel is selected." " " (em "Actions") " allow to modify this list to a certain degree.") (p "Which actions are allowed depends on the context." " " "However, actions are further separated into " (em "parameter action") " and " (em "aggregate actions") "." " " "A parameter action just sets a parameter for an aggregate action." " " "An aggregate action transforms the list of selected zettel into a different, aggregate form." " " "Only the first aggregate form is executed, following aggregate actions are ignored.") (p "In most contexts, valid actions include the name of metadata keys, at least of type " (a (@ (href . "00001006035500")) "Word") " or " (a (@ (href . "00001006034000")) "TagSet") ".") (p "To allow some kind of backward compatibility, an action written in uppercase letters that leads to an empty result list, will be ignored." " " "In this case the list of selected zettel is returned."))