function isNull ( obj )
{
	if ( obj == "" )
		return true;
	return false;
}
	
function isEmail ( obj )
{
	if (( obj.indexOf ( "@" ) == -1 ) || ( obj.indexOf ( "." ) == -1 )) {
		return false;
	}
	return true;
}

function isPositive ( obj ) {
	if ( obj.value == "" )
		return true;
	if (  isNaN(parseInt(obj.value)) ) {
		return false;
	} else if ( !(  parseInt(obj.value) > 0 )) {
		return false;
	} else {
		true;
	}
}

function montharr(m0, m1, m2, m3, m4, m5, m6, m7, m8, m9, m10, m11) {
	this[0] = m0;
      this[1] = m1;
      this[2] = m2;
      this[3] = m3;
      this[4] = m4;
      this[5] = m5;
      this[6] = m6;
      this[7] = m7;
      this[8] = m8;
      this[9] = m9;
      this[10] = m10;
      this[11] = m11;
}

function checkDate(obj) { 
 if ( !(obj.length == 10) )
		return false;
	var monthDays = new montharr(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
      var year =  parseInt ( obj.substring(0,4) );
      var month;
	if ( obj.value.substring(5,6) == "0" )
		month = parseInt ( obj.substring(6,7) ) - 1;
	else
		month = parseInt ( obj.substring(5,7) ) - 1;

	var day;
	if ( obj.value.substring(8,9) == "0" )
		day =   parseInt ( obj.substring(9,10) );
	else
		day =   parseInt ( obj.substring(8,10) );
	if ( (year>=2100) || (1900>=year) ) {
		return false;
	}
	if ( (month>11) || (0>month) ) {
		return false;
	}
      if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))
		monthDays[1] = 29;
	var nDays = monthDays[month];
	if ( (day>nDays) || (1>day) ) {
		return false;
	}
	return true;
}

        function checkYearMonth ( obj ) {
          if ( obj!= "" ) {
            if ( !(obj.length == 4) && !(obj.length == 7) )
                  return false;
            var year =  parseInt ( obj.substring(0,4) );
            if ( (year>=2100) || (1900>=year) ) {
               return false;
            }
            if ( obj.length == 4 )
		   return true;
            if ( !(obj.length == 7) )
                  return false;
           var month;
		if ( obj.substring(5,6) == "0" )
			month = parseInt ( obj.substring(6,7) ) - 1;
		else
			month = parseInt ( obj.substring(5,7) ) - 1;
            if ( (month>11) || (0>month) ) {
               return false;
            }
          }
          return true;
        }