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enableWhen & visibility

Any item — a question, a display note or a whole group — can be shown or hidden based on the answers to other questions. This is configured in the item's Show When editor and maps to FHIR's item.enableWhen / enableBehavior, with an optional SDC enableWhenExpression for advanced cases.

Opening the editor

Each item in the builder tree has a Show When control. Opening it shows the "Show When" dialog with three parts: a behaviour selector, a list of conditions, and an advanced FHIRPath field.

Conditions

Click + Add condition to add a rule. Each condition row has three parts:

  1. Question — the item whose answer to test (referenced by its linkId).
  2. Operator — the comparison, which adapts to the selected question's answer type.
  3. Value — the value to compare against (an option, number, date, etc.).

Use the ✕ button to remove a condition.

Operators by answer type

The operators offered depend on the type of the question you pick:

Question type Operators offered
Boolean (checkbox) is Yes (checked), is No (unchecked), has answer, has no answer
Choice (radio, drop-down, checklist, open-choice) =, ≠, has answer, has no answer — value picked from the question's options; the picked option's code system is saved with the condition
Integer / decimal / number =, ≠, >, <, >=, <= with a numeric value; numbers are compared as numbers, so an answer of 1.0 equals a condition of 1
Quantity numeric comparison plus a unit
Date / dateTime / time comparison operators with a date/time picker

has answer / has no answer map to the FHIR exists operator.

A condition that has no operator, an unknown operator, or no value to compare with is reported as an error when you validate or export, because FHIR requires all of them.

ALL vs ANY

The Show when … conditions are met selector at the top sets item.enableBehavior:

  • ALL (AND) — every condition must be true.
  • ANY (OR) — at least one condition must be true.

For a question that repeats, a condition is considered met if any of its answers satisfies it (per the FHIR R4 rule).

When not visible

The When not visible selector controls what happens to an item whose condition is not met. It maps to the disabledDisplay field (native in FHIR R5; on R4/R4B the builder stores it in its own extension):

  • Show grayed (protected) — the item stays on screen, greyed out and read-only.
  • Remove from view (hidden) — the item is removed from the form entirely.

FHIRPath expression (advanced)

Below the condition list is an enableWhenExpression (SDC) field. Instead of (or in addition to) the simple condition rows, you can supply a FHIRPath expression that returns a boolean, for example:

%age > 18 and %gender = 'male'

The expression is evaluated against the live QuestionnaireResponse with the same variable environment used elsewhere in the runtime. If an enableWhen list is present it takes precedence; the expression is used when no simple conditions are defined.

Build it visually

You don't have to write the FHIRPath by hand. Next to the field is a 🧩 Build… button that opens a condition builder. It shows the condition as a tree: nested ALL (AND) / ANY (OR) groups, each leaf a single rule (pick a question, a comparison or "has answer" / "has no answer", and a value — or edit that one leaf as text). Every node shows a live ✓/✗ result. Add conditions and sub-groups, and press Apply to drop the generated expression into the field. Opening the builder on an existing expression reads it back into the tree, so even complex conditions stay visible and editable.

Copying to other items

The Show When dialog can copy the current visibility setup — conditions, behaviour, disabled-display and expression — onto other items in one step, so a group of questions can share the same rule.

Live preview

The right-hand preview evaluates visibility on every edit. Items whose condition is not met are hidden or greyed according to your When not visible choice. Note that a hidden item still participates in calculatedExpression and enableWhen logic — it is only removed from what the user sees.

Next: FHIRPath expressions.