the following document crashes librsvg:

<?xml version='1.0'?>

<svg xmlns='http://www.w3.org/2000/svg'>
  <style type='text/css'>
    path
    {
      marker-start: url(#ouch);
    }
  </style>
  <marker id='ouch'>
    <path d='M 0 0 V 4'/>
  </marker>

  <path d='M 0 0 V 4'/>
</svg>

the problem is that the stylesheet is matching the <path> statement inside the <marker>.  this causes an infinite recursion as the marker is applied to itself...