Before revision:  In particular, for this purpose we put forward the {\em  Jensen-Shannon divergence (JSD){\cal   as a metric , which is bounded and has an intuitive information-theoretic interpretation .
After revision:  In particular, for this purpose we put forward the {\em Jensen-Shannon divergence (JSD){\cal as a metric , which is bounded , and is a natural generalisation of the Jensen-Shannon divergence .