<iff>

<iff> (필요충분조건) 이중 조건 요소에서 결론과 조건을 분리한다. [18.11 Feature System Declaration]
모듈iso-fs — Feature Structures
속성att.global (@xml:id, @n, @xml:lang, @rend, @style, @rendition, @xml:base, @xml:space) (att.global.linking (@corresp, @synch, @sameAs, @copyOf, @next, @prev, @exclude, @select)) (att.global.analytic (@ana)) (att.global.facs (@facs)) (att.global.change (@change))
에 의해 포함된
iso-fs: bicond
포함할 수 있다공백 요소
선언

<rng:element name="iff">
 <rng:ref name="att.global.attributes"/>
 <rng:ref name="att.global.linking.attributes"/>
 <rng:ref name="att.global.analytic.attributes"/>
 <rng:ref name="att.global.facs.attributes"/>
 <rng:ref name="att.global.change.attributes"/>
 <rng:empty/>
</rng:element>
element iff
{
   att.global.attributes,
   att.global.linking.attributes,
   att.global.analytic.attributes,
   att.global.facs.attributes,
   att.global.change.attributes,
   empty
}
예
<bicond>
 <fs>
  <f name="FOO">
   <symbol value="42"/>
  </f>
 </fs>
 <iff/>
 <fs>
  <f name="BAR">
   <binary value="true"/>
  </f>
 </fs>
</bicond>