[ros-users] URDF Anchor/Joint_Properties

Hey all,
I was looking thorugh the URDF/xacro for the Erratic and noticed two
features of the joints that I can't find documentation for: anchor and
joint_properties

    <joint name="${parent}_${suffix}_wheel_joint" type="continuous">
      <origin xyz="0 ${reflect*caster_wheel_offset_y} ${wheel_radius}"
rpy="0 0 0" />
      <axis xyz="0 1 0" />
      <anchor xyz="0 0 0" />
      <limit effort="100" velocity="100" />
      <joint_properties damping="0.0" friction="0.0" />
      <parent link="${parent}" />
      <child link="${parent}_${suffix}_wheel_link" />
    </joint>

I can't find any reference to the anchor tag anywhere.
joint_properties also seems to have the same field has the dynamics
tag. Does anyone have any more information on the first (is it
deprecated now?) and which form is correct for the second one?

Thanks,
David!!