API Reference > imodeljs-backend > ElementAspects > ExternalSourceAspect > version version version: undefined | string An optional value that is typically a version number or a pseudo version number like last modified time. It will be used by the synchronization process to detect that a source object is unchanged so that computing a cryptographic hash can be avoided. If present, this value must be guaranteed to change when any of the source object's content changes. Defined in core/backend/src/ElementAspect.ts Line 171 Last Updated: 12 June, 2024