<input ... onkeypress="sjbjl_checkfield(object,event,'minl=nn,maxl=mm,mandatory=true,valuetype=tipodidato,label=etichetta');" />

<form action="login.php" name="loginform" id="loginform" method="post" onsubmit="return checkform(this.id);"> <fieldset> <input type="text" name="username" id="username" class="text" onkeypress="sjbjl_checkfield(this,event,'minl=6,maxl=24,mandatory=true,valuetype=alfanum,label=username');" /> <input type="password" name="password" id="password" class="text" onkeypress="sjbjl_checkfield(this,event,'minl=6,maxl=24,'mandatory=true,valuetype=password,label=password');" /> <input type="submit" name="submit" id="submit" value="login" /> </fieldset> </form>