First of all there are limeted number of symbols which can be used for subscription. There are these symbols: 1 - 'u2081' 2- 'u2082' 3- 'u2083' ... 9 - 'u2089' + - 'u208A' - - 'u208B' = - 'u208C' ( - 'u208D' ) - 'u208E'