what's the lower and upper limit for a floating joint in urdf?

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Hi all,

I intend to use a floating joint in my model, and give a certain limit (t_ll, t_ul) to the translation freedom and another certain limit (r_ll, r_ul) to the rotation freedom.

But in the floating joint example , there is only one lower and one upper limit: <limit effort="30" velocity="1.0" lower="-2.2" upper="0.7" />. What do these two limits mean? Can I set two limit ranges (t_ll, t_ul) and (r_ll, r_ul)?

Thanks for any suggestion!