Schematron
Schematron is a rule-based validation language for XML documents, used to check constraints and business rules that are difficult or impossible to express with traditional schema languages like XML Schema or DTD. It operates by applying XPath expressions to XML documents to assert patterns and report errors or warnings, making it highly flexible for complex validation scenarios. It is often used in conjunction with other schema languages to provide additional validation layers.
Developers should learn Schematron when they need to validate XML documents against complex business rules, such as ensuring data integrity, compliance with industry standards, or specific document structures that go beyond basic syntax. It is particularly useful in domains like publishing, healthcare (e.g., HL7), and government data exchange, where XML documents must adhere to strict, nuanced requirements. Use cases include validating invoices, medical records, or legal documents where conditional logic and contextual checks are essential.