in command.py, why self.body_pos_relative_w and self.body_pos_relative_w does not design in form of pure global or pure local forms

[nuliguangxiaoyang-crypto]

@qiayuanl Hello,
In command.py,

        delta_pos_w = robot_anchor_pos_w_repeat
        delta_pos_w[..., 2] = anchor_pos_w_repeat[..., 2]
        delta_ori_w = yaw_quat(
            quat_mul(robot_anchor_quat_w_repeat,
                     quat_inv(anchor_quat_w_repeat)))

        self.body_quat_relative_w = quat_mul(delta_ori_w, self.body_quat_w)
        self.body_pos_relative_w = delta_pos_w + quat_apply(
            delta_ori_w, self.body_pos_w - anchor_pos_w_repeat)

in commands.py, we can see in the delta_pos_w, z get from refer_anchor z ,but xy get from real robot xy,
and why here body_pos_relative_w and body_pos_relative_w design as the upper code ,but bot pure global or pure local forms.
What 's the reasoning behind this design? Thanks!