extract_nt.xbgf

<xbgf:sequence
  xmlns:bgf="http://planet-sl.org/bgf"
  xmlns:xbgf="http://planet-sl.org/xbgf">
  <xbgf:extract>
    <bgf:production>
      <nonterminal>xs</nonterminal>
      <bgf:expression>
        <star>
          <bgf:expression>
            <nonterminal>x</nonterminal>
          </bgf:expression>
        </star>
      </bgf:expression>
    </bgf:production>
    <in>
      <nonterminal>a</nonterminal>
    </in>
  </xbgf:extract>
</xbgf:sequence>