mujoco

<mujoco>
  <compiler discardvisual="true"/>

  <asset>
    <texture name="discarded_skybox" type="skybox" builtin="gradient"
             rgb1=".3 .5 .7" rgb2="0 0 0" width="32" height="512"/>

    <texture name="discarded" type="2d" builtin="checker" width="512" height="512" rgb1=".1 .2 .3" rgb2=".2 .3 .4"/>
    <material name="discarded" texture="discarded" texrepeat="1 1" texuniform="true" reflectance=".2"/>

    <mesh name="kept" vertex="0 0 0  1 0 0  0 1 0  0 0 1"/>
    <mesh name="discarded0" vertex="0 0 0  1 0 0  0 1 0  0 0 1"/>
    <mesh name="discarded1" vertex="0 0 0  1 0 0  0 1 0  0 0 1"/>
  </asset>

  <worldbody>
    <geom name="kept_floor" size="0 0 .05" type="plane" material="discarded"/>

    <body pos="0 0 -.5">
      <freejoint/>
      <geom name="discarded0" type="mesh" mesh="discarded0" contype="0" conaffinity="0"/>
    </body>

    <site name="tendon0" pos=".1 0 1.5"/>
    <geom name="kept_tendon" size="0.2" contype="0" conaffinity="0" pos="0 0 1"/>
    <body pos=".1 0 -.5">
      <site name="tendon1" pos="0 0 1"/>
      <freejoint/>
      <geom name="discarded1" type="mesh" mesh="kept" contype="0" conaffinity="0"/>
    </body>

    <body pos=".2 0 -.5">
      <geom name="kept0" type="mesh" mesh="kept"/>
    </body>

    <body pos=".3 0 -.5">
      <freejoint/>
      <geom name="kept1" type="mesh" mesh="kept"/>
    </body>

    <body pos=".4 0 -.5">
      <geom name="discarded2" type="mesh" mesh="kept" contype="0" conaffinity="0"/>
    </body>

    <geom name="kept_sensor" size="0.2" contype="0" conaffinity="0"/>

    <geom name="kept_pair" size="0.2" contype="0" conaffinity="0" pos=".3 0 .4"/>

    <geom name="kept_tuple" size="0.2" contype="0" conaffinity="0"/>
  </worldbody>

  <contact>
    <pair geom1="kept1" geom2="kept_pair"/>
  </contact>

  <tendon>
    <spatial range="0 1">
      <site site="tendon0"/>
      <geom geom="kept_tendon"/>
      <site site="tendon1"/>
    </spatial>
  </tendon>

  <sensor>
    <framepos objtype="geom" objname="kept_sensor"/>
  </sensor>

  <custom>
    <tuple name="tuple">
      <element objtype="geom" objname="kept_tuple"/>
    </tuple>
  </custom>
</mujoco>