schematron 0.16.1

Schematron: pure Rust implementation of ISO/IEC 19757-3 rule-based XML validation, with its own XML parser, XPath 1.0 engine, XPath 2.0 and 3.0 subsets, schema linting, and SVRL reporting. By SixArm.com.
Documentation 
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<schema xmlns="http://purl.oclc.org/dsdl/schematron">
  <ns prefix="inv" uri="http://example.com/invoice"/>
  <pattern>
    <rule context="inv:invoice">
      <assert test="inv:total">An invoice needs a total.</assert>
    </rule>
  </pattern>
</schema>