<elementRef>

<elementRef> points to the specification for some element which is to be included in a schema. [23.2 Modules and Schemas]
Module tagdocs — Documentation Elements
Attributes
key⚓︎ the identifier used for the required element within the source indicated.
Status Required
Datatype teidata.xmlName
Member of
model.contentPart model.oddRef
Contained by
tagdocs: alternate content schemaSpec sequence specGrp
May contain Empty element
Note

Elements are identified by the name supplied as value for the ident attribute on the elementSpec element in which they are declared. TEI element names are unique.
Example
<elementRef key="p"/>

Include in the schema an element named p available from the current default source.
Example
<elementRef key="p" source="tei:1.2.1"/>

Include in the schema an element named p available from the TEI P5 1.2.1 release.
Schematron

<sch:pattern>
<sch:rule context="tei:elementRef[ parent::tei:schemaSpec | parent::tei:specGrp ]">
 <sch:report test="@minOccurs | @maxOccurs"
  role="error">An element reference is not repeatable when part of a schema specification (and thus this <elementRef> should not have @minOccurs or @maxOccurs).</sch:report>
</sch:rule>
<sch:rule context="tei:content//tei:elementRef">
 <sch:report test="@source" role="error">An element reference within a content model must refer to a locally defined element specification (and thus this <elementRef> should not have @source).</sch:report>
</sch:rule>
</sch:pattern>
Content model 
<content>
 <empty/>
</content>
Schema Declaration 
<rng:element name="elementRef">
 <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:ref name="att.repeatable.attributes"/>
 <rng:attribute name="key">
  <rng:ref name="teidata.xmlName"/>
 </rng:attribute>
 <rng:empty/>
</rng:element>
element elementRef
{
   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,
   att.repeatable.attributes,
   attribute key { teidata.xmlName },
   empty
}