I Built a VS Code Extension That Validates VAST XML as You Type

If you work in ad tech you've probably seen VAST XML. It's the IAB standard that carries every video and CTV ad impression: the tag that tells a player what to show, where to fire tracking pixels, and how to handle wrappers. $30B+ in annual US ad spend runs through it. It's also surprisingly easy to ship a broken one. The spec is six versions deep (2.0 through 4.3), touches several other standards (XML, RFC 3986, IANA media types, ISO 4217), and the tooling for validating it has historically bee