function checkDate( day,month,year) {
  de = document.getElementById( day );
  me = document.getElementById( month );
  ye = document.getElementById( year );
  sm = me.selectedIndex;
  sy = ye.options[ye.selectedIndex].value;


  if ( me.selectedIndex == 2 ) {
    isLeap = (sy % 4 == 0 && (sy % 400 == 0 || sy % 100 != 0) );
    if ( isLeap ) {
      if ( de.options.length == 29 )
        de.options[29] = new Option('29','29')
      else {
        if ( de.selectedIndex > 29 )
          de.selectedIndex = 29;
        de.options.length = 30;
      }
    } else {
      if ( de.options.selectedIndex > 28 )
        de.options.selectedIndex = 28;
      de.options.length = 29;
    }
  } else {
    if ( de.options.length < 31 ) {
      for( i=de.options.length;i<=31;i++ )
        de.options[i] = new Option(i,i );
    }
    is30 = ( sm == 4 || sm == 6 || sm == 9 || sm == 11 );
    if ( is30 && de.options.length == 32 ) {
      if(de.selectedIndex == 31 )
        de.selectedIndex = 30;
      de.options.length--;
    } else if ( !is30 && de.options.length == 31 ) {
      de.options[31]=new Option('31','31');
    }
  }
}

function clearFecha( nombre ) {
  dd = document.getElementById( nombre+"_day" );
  mm = document.getElementById( nombre+"_month" );
  yy = document.getElementById( nombre+"_year" );
  dd.selectedIndex = mm.selectedIndex = yy.selectedIndex = 0;
}