TEI: Guidelines for Electronic Text Encoding and Interchange

<constraintSpec ident="isoconstraint"
scheme="schematron">
<constraint>
<sch:rule context="tei:constraint">
<sch:assert test="tei:fileDesc/tei:titleStmt/tei:title[ @type eq 'main']">a main title must be supplied</sch:assert>
</sch:rule>
</constraint>
</constraintSpec>

<constraintSpec ident="local"
scheme="private">
<constraint>
(output = (ident(title) ident(author) "You must supply a title or an author"))
</constraint>
</constraintSpec>

XML syntaxCompact syntax

<rng:element name="constraint">
 <rng:ref name="att.global.attributes"/>
 <rng:ref name="att.global.analytic.attributes"/>
 <rng:ref name="att.global.change.attributes"/>
 <rng:ref name="att.global.facs.attributes"/>
 <rng:ref name="att.global.linking.attributes"/>
 <rng:ref name="att.global.rendition.attributes"/>
 <rng:ref name="att.global.responsibility.attributes"/>
 <rng:ref name="att.global.source.attributes"/>
 <rng:zeroOrMore>
 <rng:choice>
  <rng:text/>
  <rng:ref name="anyElement_constraint_5"/>
 </rng:choice>
 </rng:zeroOrMore>
</rng:element>

element constraint
{
 att.global.attributes,
 att.global.analytic.attributes,
 att.global.change.attributes,
 att.global.facs.attributes,
 att.global.linking.attributes,
 att.global.rendition.attributes,
 att.global.responsibility.attributes,
 att.global.source.attributes,
 ( text | anyElement_constraint_5 )*
}