This example references a definition of a measurement unit declared in the TEI Header:
<measure type="weight"> <num>2</num> pounds of flesh </measure> <measure type="currency">£10-11-6d</measure> <measure type="area" unitRef="#merk">2 <unit>merks</unit> of old extent</measure> <!-- In the TEI Header: --> <encodingDesc> <unitDecl> <unitDef xml:id="merk" type="area"> <label>merk</label> <placeName ref="#Scotland"/> <desc>A merk was an area of land determined variably by its agricultural productivity.</desc> </unitDef> </unitDecl> </encodingDesc>