Language Resource Management -- Morpho-syntactic Annotation Framework (MAF)

<rng:element name="transition">
<rng:optional>
 <rng:attribute name="source">
  <rng:ref name="macro.fsm.state"/>
 </rng:attribute>
</rng:optional>
<rng:optional>
 <rng:attribute name="target">
  <rng:ref name="macro.fsm.state"/>
 </rng:attribute>
</rng:optional>
<rng:choice>
 <rng:ref name="token"/>
 <rng:ref name="wordForm"/>
 <rng:ref name="wfAlt"/>
</rng:choice>
</rng:element>

element transition
{
   attribute source { macro.fsm.state }?,
   attribute target { macro.fsm.state }?,
   ( token | wordForm | wfAlt )
}