With a [[list of zettel identifier|00001007710000]], a [[query directives|00001007720000]], or a [[search expression|00001007701000]], a list of zettel is selected.
__Actions__ allow to modify this list to a certain degree.

Which actions are allowed depends on the context.
However, actions are further separated into __parameter action__ and __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.

In most contexts, valid actions include the name of metadata keys, at least of type [[Word|00001006035500]] or [[TagSet|00001006034000]].

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.