---
type: "sdc-page"
title: "SDC: StructureDefinition-sdc-questionnaire-initialExpression-intro"
source: "sdc/input/pagecontent/StructureDefinition-sdc-questionnaire-initialExpression-intro.xml"
---
# SDC: StructureDefinition-sdc-questionnaire-initialExpression-intro

Additional details on the use of this extension can be found on the [Form Behavior](/sdc-behavior#initialExpression), [Questionnaire Population](/sdc-populate#expression-based-population), and [Data Extraction](/sdc-extraction) pages. For guidance on using `initialExpression` refer to the [Expressions page - initialExpression](/sdc-expressions#initialExpression) section.