A streaming Schematron

records.sch

<sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt3"
            xmlns:xs="http://www.w3.org/2001/XMLSchema"
            xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <sch:ns prefix="mets" uri="http://www.loc.gov/METS/"/>
  <sch:ns prefix="oai" uri="http://www.openarchives.org/OAI/2.0/"/>
  <sch:ns prefix="xs" uri="http://www.w3.org/2001/XMLSchema"/>
  <xsl:accumulator name="recordId" streamable="yes" initial-value="()" as="xs:string?">
    <xsl:accumulator-rule match="oai:identifier/text()" select="."/>
  </xsl:accumulator>
  <sch:pattern>
    <sch:rule context="mets:fileSec" streaming="true" burst="snapshot">
      <sch:report test="mets:fileGrp[@USE = 'ZOOM']">IIIF-Interface for record <sch:value-of select="accumulator-after('recordId')"/></sch:report>
    </sch:rule>
  </sch:pattern>
</sch:schema>