Best practice suggests the use of controlled vocabulary for the currency attribute, such as the ISO 4217 list of currency designators.
<elementSpec xmlns="http://www.tei-c.org/ns/1.0" rend="add" ident="price" module="MEI.header"><desc xml:lang="en">The cost of access to a bibliographic item.</desc>
<classes>
<memberOf key="att.common"/>
<memberOf key="att.bibl"/>
<memberOf key="att.lang"/>
<memberOf key="model.titlePagePart"/>
</classes>
<content>
<sequence minOccurs="1" maxOccurs="1"><classRef key="model.headLike" minOccurs="0" maxOccurs="unbounded"/>
<alternate minOccurs="0" maxOccurs="unbounded"><textNode/>
<classRef key="model.textPhraseLike.limited"/></alternate></sequence>
</content>
<attList><attDef ident="amount" usage="opt">
<desc xml:lang="en">Numeric value capturing a cost. Can only be interpreted in combination with the
currency attribute.</desc>
<datatype>
<dataRef name="decimal">
<dataFacet name="pattern" value="[0-9]+\.[0-9]{2}"/>
</dataRef>
</datatype>
</attDef>
<attDef ident="currency" usage="opt">
<desc xml:lang="en">Monetary unit.</desc>
<datatype>
<dataRef name="NMTOKEN"/>
</datatype>
</attDef></attList>
<remarks xml:lang="en">
<p>Best practice suggests the use of controlled vocabulary for the currency attribute,
such as
the ISO 4217 list of currency designators.</p>
</remarks></elementSpec>