E</code> keyword
        specifies the release point (starting from 0). The default is -1 that
        means "envelope without sustain".
      </p>

      <p>
        If the <code>:LOOP-NODE</code> keyword has a non negative value, it is
        the starting point of the loop of the segments during the sustain phase
        of the envelope. The ending point is the point that precedes the release
        point.
      </p>

      <p>
        <code>BREAKPOINTS->ENV</code> and <code>FREQ-BREAKPOINTS->ENV</code>