Schematron as XSLT Interface, and Advanced Validation Models

Schematron (ISO/IEC 19757-3:2008, 2016, 2020) is widely enjoyed as perhaps the most expressive and powerful of all XML schema languages. In this article, I argue that Schematron is profitably seen as a kind of API (application programming interface) for a constrained flavor of XSLT. This outlook has immense benefits, because when we act on that insight, Schematron’s horizons expand to those of XSLT. Anything an XSLT can create can be reported in Schematron, and together they can conquer the world. I present four models of validation that closely partner XSLT and Schematron, and offer suggestions on how that partnership can be strengthened in the future.