The lb element is allowed here in order to facilitate karaoke applications.
<elementSpec ident="refrain" module="MEI.lyrics">
<desc xml:lang="en">Recurring lyrics, especially at the end of each verse or stanza of a poem or song
lyrics;
a chorus.</desc>
<classes>
<memberOf key="att.common"/>
<memberOf key="att.facsimile"/>
<memberOf key="att.lang"/>
<memberOf key="att.refrain.log"/>
<memberOf key="att.refrain.vis"/>
<memberOf key="att.refrain.ges"/>
<memberOf key="att.refrain.anl"/>
<memberOf key="model.verseLike"/>
</classes>
<content>
<rng:zeroOrMore>
<rng:choice>
<rng:ref name="dir"/>
<rng:ref name="dynam"/>
<rng:ref name="tempo"/>
<rng:ref name="space"/>
</rng:choice>
</rng:zeroOrMore>
<rng:oneOrMore>
<rng:choice>
<rng:ref name="volta"/>
<rng:ref name="model.sylLike"/>
<rng:ref name="model.appLike"/>
<rng:ref name="model.editLike"/>
</rng:choice>
</rng:oneOrMore>
</content>
<remarks xml:lang="en">
<p>The <gi scheme="MEI">lb</gi> element is allowed here in order to facilitate karaoke applications.</p>
</remarks>
</elementSpec>