Include the constraint http://hl7.org/fhir/extension-questionnaire-constraint.html on the using expressions guidance page.

Also need to provide some additional guidance on the usage of the location property in this constraint.

{
"resourceType": "OperationOutcome",
"issue": [
{
"severity": "error",
"code": "required",
"details":

,
"location": [
"QuestionnaireResponse.item[0].item[0].item[1].answer[0]", // review date
"QuestionnaireResponse.item[0].item[0].item[2].item[1].answer[0]", // start period
"QuestionnaireResponse.item[0].item[0].item[2].item[2].answer[0]" // end period
]
},

// definition
<item (item[0].item[0])>
<type value=group/>
<extension url="location" >
<valueString value="item[1].answer[0]"/>
<valueString value="item[2].item[1].answer[0]"/>
<valueString value="item[2].item[2].answer[0]"/>
</extension>
</item>