mujoco

<mujoco>
  <!-- use Runge-Kutta for better energy conservation -->
  <option integrator="RK4">
    <flag energy="enable"/>
  </option>

  <statistic center="0 0 0"/>

  <worldbody>
    <site name="origin" size=".01" rgba="1 0 0 1"/>
    <light pos="0 0 3"/>

    <body pos="1 0 .06">
      <joint type="slide" axis="1 0 0"/>
      <geom size=".05"/>
      <site name="attachment" size=".01" pos="0 0 -.06" rgba="1 0 0 1"/>
    </body>
  </worldbody>

  <tendon>
    <spatial name="tendon" stiffness="10" springlength="0 .5">
      <site site="origin"/>
      <site site="attachment"/>
    </spatial>
  </tendon>

  <sensor>
    <tendonpos tendon="tendon"/>
  </sensor>
</mujoco>