Restriction Tag Expression

Context: HL Kit … Kit Reference … Tag Expression Types 

The role of the Restriction tag expression is to further limit the set of things or picks that are made available for selection.

determine whether a pick or thing should be included in a choose form. The choose form contains the list of picks/things from which the user can select when adding items to a portal (i.e. dynamic table, chooser, or thing-based menu). If the tag expression is satisfied, then the pick/thing is shown within the list of options and can be added by the user. Otherwise, the pick/thing is omitted from the available list.

The Candidate tag expression is always applied against the pick/thing itself. The tag expression is compared against all of the tags possessed by the object. For picks, this includes the effects of all dynamically assigned and deleted tags. The Candidate tag expression is only invoked when the user triggers the portal to display the list of options to choose from. Consequently, the tags used for picks are the final set of tags after evaluation completes. This also means that picks can dynamically change their state and change whether they appear as valid choices within a given portal.

The "restriction" element defines a Restriction Tag Expression for the portal that further limits the set of things/picks that are available for selection. This tag expression is compared against all picks that already exist within the container. Any object that exists within the restricted list is precluded from being selected again, resulting in it being omitted from the list of available choices. The complete list of attributes for this element is below.