Metadata that defines how information within health documents or datasets is internally organised and structured. It enables access to specific sections within complex clinical documents and ensures consistent parsing across systems. It includes document schema , template identifiers, section headings and hierarchies, FHIR resource references, and linkage to terminologies and code systems (e.g. SNOMED CT, LOINC). It maps to HL7 FHIR StructureDefinition and Composition resources.