<?xml version="1.0" ?>
<sdf version='1.7'>
  <world name="world_frame_invalid_attached_to">

    <frame name="F" attached_to="A"/>                     <!-- INVALID: no sibling frame named A. -->
    <frame name="self_cycle" attached_to="self_cycle"/>   <!-- INVALID: graph cycle when frame attached_to itself. -->

  </world>
</sdf>
