[xsl] Truncate input

[<m.core@xxxxxxxxxxxxxxxx>]

Hi all,

i need to truncate input that can be write in a box i have a var v1=2 if after coma there is more then v1 numbers then it must be truncate to v1 es...

if i insert 3,45678 in the input it let me write only 3,45 because v1=2 

i think this must be done in the tags <input > </input>
i'm already in the case that the number is real ecc..

How can i do?..is there an option like <input format="">?

thx for replies