fonttools/Lib/fontTools/feaLib/testdata/GSUB_3.ttx

<?xml version="1.0" encoding="UTF-8"?>
<ttFont>

  <GSUB>
    <GSUB>
      <Version value="1.0"/>
      <ScriptList>
        <!-- ScriptCount=0 -->
      </ScriptList>
      <FeatureList>
        <!-- FeatureCount=2 -->
        <FeatureRecord index="0">
          <FeatureTag value="f1  "/>
          <Feature>
            <!-- LookupCount=1 -->
            <LookupListIndex index="0" value="0"/>
          </Feature>
        </FeatureRecord>
        <FeatureRecord index="1">
          <FeatureTag value="f2  "/>
          <Feature>
            <!-- LookupCount=1 -->
            <LookupListIndex index="0" value="0"/>
          </Feature>
        </FeatureRecord>
      </FeatureList>
      <LookupList>
        <!-- LookupCount=1 -->
        <AlternateSubst index="0" Format="1">
          <AlternateSet glyph="A">
            <Alternate glyph="A.alt1"/>
            <Alternate glyph="A.alt2"/>
          </AlternateSet>
          <AlternateSet glyph="B">
            <Alternate glyph="B.alt1"/>
            <Alternate glyph="B.alt2"/>
            <Alternate glyph="B.alt3"/>
          </AlternateSet>
          <AlternateSet glyph="C">
            <Alternate glyph="C.alt1"/>
          </AlternateSet>
        </AlternateSubst>
      </LookupList>
    </GSUB>
  </GSUB>

  <GPOS>
    <GPOS>
      <Version value="1.0"/>
      <ScriptList>
        <!-- ScriptCount=0 -->
      </ScriptList>
      <FeatureList>
        <!-- FeatureCount=0 -->
      </FeatureList>
      <LookupList>
        <!-- LookupCount=0 -->
      </LookupList>
    </GPOS>
  </GPOS>

</ttFont>