Live Tag Expression

Context: HL Kit … Kit Reference … Tag Expression Types 

The role of the Live tag expression is to determine whether a visual element should be considered "live". When a visual element is "live", it is fully operational within the interface. When non-live, a visual element is treated as if it does not exist, being omitted from display and not processed in any way. All attempts to manipulate a non-live visual element via scripts are simply ignored.

The Live tag expression is always applied against the container whose information is to be displayed within the visual element. This will typically be the currently active actor, although it will sometimes be a gizmo (when editing a gizmo) or a different actor (when displaying material in places like the Dashboard). The tag expression is compared against all of the tags possessed by the container at the conclusion of the evaluation cycle, so the effects of all dynamically assigned and deleted tags are included. If the tag expression is satisfied, the visual element is considered live and shown normally. Otherwise, the visual element is deemed non-live and hidden from display.

The Live tag expression is applied anew after every evaluation cycle. Consequently, it is possible to have visual elements dynamically appear and disappear in response to user actions. This can range from a simple portal changing state to an entire tab panel or summary panel transitioning its state.