<svg width="4in" height="3in">

  <defs>

    <symbol id="Triangle" min-x="0" min-y="0" max-x="100" max-y="100" ref-x="0" ref-y="50">

      <path d="M 0 0 L 0 100 L 100 50 z"/>

    </symbol>

  </defs>

  <desc>An double-headed arrow example using markers

  </desc>

  <path d="M0 0">

         beginning of the path -->

    <marker href="#Triangle" width="200" height="200" style="text-transform: rotate(180)"/>

    <data d="M 2000 2000"/>

    <marker href=""/>

    <data d="L 4000 2000 L 4000 4000"/>

    <marker href="#Triangle" width="200" height="200"/>

    <data d="L 6000 4000"/>

  </path>

</svg>