How vastlint's Validation Rules Were Extracted from the VAST PDF Specs and XSD Schemas

The IAB Tech Lab publishes VAST as two artifacts: a PDF specification document and a set of XSD schema files. The PDF is the normative authority. It defines what a conformant VAST response must, should, and may contain. The XSD describes the document structure in machine-readable form but has gaps; it does not cover business logic, ordering constraints, or anything involving URLs. Building a linter against VAST meant reading both and treating them as complementary sources of truth, not interchan