var digits = "0123456789";
var lowercaseLetters = "abcdefghijklmnopqrstuvwxyz"
var uppercaseLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
var whitespace = " \t\n\r";
var decimalPointDelimiter = "."
var mPrefix = "You did not enter a value into the "
var mSuffix = " field. This is a required field. Please enter it now."
var sUSLastName = "Last Name"
var sUSFirstName = "First Name"
var sWorldLastName = "Family Name"
var sWorldFirstName = "Given Name"
var sTitle = "Title"
var sCompanyName = "Company Name"
var sUSAddress = "Street Address"
var sWorldAddress = "Address"
var sCity = "City"
var sStateCode = "State Code"
var sWorldState = "State, Province, or Prefecture"
var sCountry = "Country"
var sZIPCode = "ZIP Code"
var sWorldPostalCode = "Postal Code"
var sPhone = "Phone Number"
var sFax = "Fax Number"
var sDateOfBirth = "Date of Birth"
var sExpirationDate = "Expiration Date"
var sEmail = "Email"
var sSSN = "Social Security Number"
var sCreditCardNumber = "Credit Card Number"
var sOtherInfo = "Other Information"
var iStateCode = "This field must be a valid two character U.S. state abbreviation (like CA for California). Please reenter it now."
var iZIPCode = "This field must be a 5 or 9 digit U.S. ZIP Code (like 94043). Please reenter it now."
var iUSPhone = "This field must be a 10 digit U.S. phone number (like 415 555 1212). Please reenter it now."
var iWorldPhone = "This field must be a valid international phone number. Please reenter it now."
var iSSN = "This field must be a 9 digit U.S. social security number (like 123 45 6789). Please reenter it now."
var iEmail = "This field must be a valid email address (like foo@bar.com). Please reenter it now."
var iCreditCardPrefix = "This is not a valid "
var iCreditCardSuffix = " credit card number. (Click the link on this form to see a list of sample numbers.) Please reenter it now."
var iDay = "This field must be a day number between 1 and 31.  Please reenter it now."
var iMonth = "This field must be a month number between 1 and 12.  Please reenter it now."
var iYear = "This field must be a 2 or 4 digit year number.  Please reenter it now."
var iDatePrefix = "The Day, Month, and Year for "
var iDateSuffix = " do not form a valid date.  Please reenter them now."
var pEntryPrompt = "Please enter a "
var pStateCode = "2 character code (like CA)."
var pEmail = "valid email address (like foo@bar.com)."
var pDay = "day number between 1 and 31."
var pMonth = "month number between 1 and 12."
var pYear = "2 or 4 digit year number."
var defaultEmptyOK = false
function makeArray(n) {
   for (var i = 1; i <= n; i++) {
      this[i] = 0
   } 
   return this
}

var daysInMonth = makeArray(12);
daysInMonth[1] = 31;
daysInMonth[2] = 29;   // must programmatically check this
daysInMonth[3] = 31;
daysInMonth[4] = 30;
daysInMonth[5] = 31;
daysInMonth[6] = 30;
daysInMonth[7] = 31;
daysInMonth[8] = 31;
daysInMonth[9] = 30;
daysInMonth[10] = 31;
daysInMonth[11] = 30;
daysInMonth[12] = 31;
function isEmpty(s)
{   return ((s == null) || (s.length == 0))
}
function isWhitespace (s)
{   var i;
    // Is s empty?
    if (isEmpty(s)) return true;
    for (i = 0; i < s.length; i++)
    {   
        var c = s.charAt(i);
        if (whitespace.indexOf(c) == -1) return false;
    }
    return true;
}
function stripCharsInBag (s, bag)
{   var i;
    var returnString = "";
    for (i = 0; i < s.length; i++)
    {   
        var c = s.charAt(i);
        if (bag.indexOf(c) == -1) returnString += c;
    }
    return returnString;
}
function stripCharsNotInBag (s, bag)

{   var i;
    var returnString = "";
    for (i = 0; i < s.length; i++)
    {   
        var c = s.charAt(i);
        if (bag.indexOf(c) != -1) returnString += c;
    }
    return returnString;
}
function stripWhitespace (s)
{   return stripCharsInBag (s, whitespace)
}
function charInString (c, s)
{   for (i = 0; i < s.length; i++)
    {   if (s.charAt(i) == c) return true;
    }
    return false
}
function stripInitialWhitespace (s)
{   var i = 0;
    while ((i < s.length) && charInString (s.charAt(i), whitespace))
       i++;
    return s.substring (i, s.length);
}
function isLetter (c)
{   return ( ((c >= "a") && (c <= "z")) || ((c >= "A") && (c <= "Z")) )
}
function isDigit (c)
{   return ((c >= "0") && (c <= "9"))
}
function isLetterOrDigit (c)
{   return ( isLetter(c) || isDigit(c) )
}
function isInteger (s)
{   var i;
    if (isEmpty(s)) 
       if (isInteger.arguments.length == 1) return defaultEmptyOK;
       else return (isInteger.arguments[1] == true);
    for (i = 0; i < s.length; i++)
    {   
        var c = s.charAt(i);
        if (!isDigit(c)) return false;
    }
    return true;
}
function isSignedInteger (s)
{   if (isEmpty(s)) 
       if (isSignedInteger.arguments.length == 1) return defaultEmptyOK;
       else return (isSignedInteger.arguments[1] == true);
    else {
        var startPos = 0;
        var secondArg = defaultEmptyOK;
        if (isSignedInteger.arguments.length > 1)
            secondArg = isSignedInteger.arguments[1];
        if ( (s.charAt(0) == "-") || (s.charAt(0) == "+") )
           startPos = 1;    
        return (isInteger(s.substring(startPos, s.length), secondArg))
    }
}
function isPositiveInteger (s)
{   var secondArg = defaultEmptyOK;
    if (isPositiveInteger.arguments.length > 1)
        secondArg = isPositiveInteger.arguments[1];
    return (isSignedInteger(s, secondArg)
         && ( (isEmpty(s) && secondArg)  || (parseInt (s) > 0) ) );
}
function isNonnegativeInteger (s)
{   var secondArg = defaultEmptyOK;
    if (isNonnegativeInteger.arguments.length > 1)
        secondArg = isNonnegativeInteger.arguments[1];
    return (isSignedInteger(s, secondArg)
         && ( (isEmpty(s) && secondArg)  || (parseInt (s) >= 0) ) );
}
function isNegativeInteger (s)
{   var secondArg = defaultEmptyOK;
    if (isNegativeInteger.arguments.length > 1)
        secondArg = isNegativeInteger.arguments[1];
    return (isSignedInteger(s, secondArg)
         && ( (isEmpty(s) && secondArg)  || (parseInt (s) < 0) ) );
}
function isNonpositiveInteger (s)
{   var secondArg = defaultEmptyOK;
    if (isNonpositiveInteger.arguments.length > 1)
        secondArg = isNonpositiveInteger.arguments[1];
    return (isSignedInteger(s, secondArg)
         && ( (isEmpty(s) && secondArg)  || (parseInt (s) <= 0) ) );
}
function isFloat (s)
{   var i;
    var seenDecimalPoint = false;
    if (isEmpty(s)) 
       if (isFloat.arguments.length == 1) return defaultEmptyOK;
       else return (isFloat.arguments[1] == true);
    if (s == decimalPointDelimiter) return false;
    for (i = 0; i < s.length; i++)
    {   
        var c = s.charAt(i);
        if ((c == decimalPointDelimiter) && !seenDecimalPoint) seenDecimalPoint = true;
        else if (!isDigit(c)) return false;
    }
    return true;
}







// isSignedFloat (STRING s [, BOOLEAN emptyOK])
// 
// True if string s is a signed or unsigned floating point 
// (real) number. First character is allowed to be + or -.
//
// Also returns true for unsigned integers. If you wish
// to distinguish between integers and floating point numbers,
// first call isSignedInteger, then call isSignedFloat.
//
// Does not accept exponential notation.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function isSignedFloat (s)

{   if (isEmpty(s)) 
       if (isSignedFloat.arguments.length == 1) return defaultEmptyOK;
       else return (isSignedFloat.arguments[1] == true);

    else {
        var startPos = 0;
        var secondArg = defaultEmptyOK;

        if (isSignedFloat.arguments.length > 1)
            secondArg = isSignedFloat.arguments[1];

        // skip leading + or -
        if ( (s.charAt(0) == "-") || (s.charAt(0) == "+") )
           startPos = 1;    
        return (isFloat(s.substring(startPos, s.length), secondArg))
    }
}




// isAlphabetic (STRING s [, BOOLEAN emptyOK])
// 
// Returns true if string s is English letters 
// (A .. Z, a..z) only.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.
//
// NOTE: Need i18n version to support European characters.
// This could be tricky due to different character
// sets and orderings for various languages and platforms.

function isAlphabetic (s)

{   var i;

    if (isEmpty(s)) 
       if (isAlphabetic.arguments.length == 1) return defaultEmptyOK;
       else return (isAlphabetic.arguments[1] == true);

    // Search through string's characters one by one
    // until we find a non-alphabetic character.
    // When we do, return false; if we don't, return true.

    for (i = 0; i < s.length; i++)
    {   
        // Check that current character is letter.
        var c = s.charAt(i);

        if (!isLetter(c))
        return false;
    }

    // All characters are letters.
    return true;
}




// isAlphanumeric (STRING s [, BOOLEAN emptyOK])
// 
// Returns true if string s is English letters 
// (A .. Z, a..z) and numbers only.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.
//
// NOTE: Need i18n version to support European characters.
// This could be tricky due to different character
// sets and orderings for various languages and platforms.

function isAlphanumeric (s)

{   var i;

    if (isEmpty(s)) 
       if (isAlphanumeric.arguments.length == 1) return defaultEmptyOK;
       else return (isAlphanumeric.arguments[1] == true);

    // Search through string's characters one by one
    // until we find a non-alphanumeric character.
    // When we do, return false; if we don't, return true.

    for (i = 0; i < s.length; i++)
    {   
        // Check that current character is number or letter.
        var c = s.charAt(i);

        if (! (isLetter(c) || isDigit(c) ) )
        return false;
    }

    // All characters are numbers or letters.
    return true;
}




// reformat (TARGETSTRING, STRING, INTEGER, STRING, INTEGER ... )       
//
// Handy function for arbitrarily inserting formatting characters
// or delimiters of various kinds within TARGETSTRING.
//
// reformat takes one named argument, a string s, and any number
// of other arguments.  The other arguments must be integers or
// strings.  These other arguments specify how string s is to be
// reformatted and how and where other strings are to be inserted
// into it.
//
// reformat processes the other arguments in order one by one.
// * If the argument is an integer, reformat appends that number 
//   of sequential characters from s to the resultString.
// * If the argument is a string, reformat appends the string
//   to the resultString.
//
// NOTE: The first argument after TARGETSTRING must be a string.
// (It can be empty.)  The second argument must be an integer.
// Thereafter, integers and strings must alternate.  This is to
// provide backward compatibility to Navigator 2.0.2 JavaScript
// by avoiding use of the typeof operator.
//
// It is the caller's responsibility to make sure that we do not
// try to copy more characters from s than s.length.
//
// EXAMPLES:
//
// * To reformat a 10-digit U.S. phone number from "1234567890"
//   to "(123) 456-7890" make this function call:
//   reformat("1234567890", "(", 3, ") ", 3, "-", 4)
//
// * To reformat a 9-digit U.S. Social Security number from
//   "123456789" to "123-45-6789" make this function call:
//   reformat("123456789", "", 3, "-", 2, "-", 4)
//
// HINT:
//
// If you have a string which is already delimited in one way
// (example: a phone number delimited with spaces as "123 456 7890")
// and you want to delimit it in another way using function reformat,
// call function stripCharsNotInBag to remove the unwanted 
// characters, THEN call function reformat to delimit as desired.
//
// EXAMPLE:
//
// reformat (stripCharsNotInBag ("123 456 7890", digits),
//           "(", 3, ") ", 3, "-", 4)

function reformat (s)

{   var arg;
    var sPos = 0;
    var resultString = "";

    for (var i = 1; i < reformat.arguments.length; i++) {
       arg = reformat.arguments[i];
       if (i % 2 == 1) resultString += arg;
       else {
           resultString += s.substring(sPos, sPos + arg);
           sPos += arg;
       }
    }
    return resultString;
}




// isSSN (STRING s [, BOOLEAN emptyOK])
// 
// isSSN returns true if string s is a valid U.S. Social
// Security Number.  Must be 9 digits.
//
// NOTE: Strip out any delimiters (spaces, hyphens, etc.)
// from string s before calling this function.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function isSSN (s)
{   if (isEmpty(s)) 
       if (isSSN.arguments.length == 1) return defaultEmptyOK;
       else return (isSSN.arguments[1] == true);
    return (isInteger(s) && s.length == digitsInSocialSecurityNumber)
}


// isEmail (STRING s [, BOOLEAN emptyOK])
// 
// Email address must be of form a@b.c -- in other words:
// * there must be at least one character before the @
// * there must be at least one character before and after the .
// * the characters @ and . are both required
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function isEmail (s)
{   if (isEmpty(s)) 
       if (isEmail.arguments.length == 1) return defaultEmptyOK;
       else return (isEmail.arguments[1] == true);
   
    // is s whitespace?
    if (isWhitespace(s)) return false;
    
    // there must be >= 1 character before @, so we
    // start looking at character position 1 
    // (i.e. second character)
    var i = 1;
    var sLength = s.length;

    // look for @
    while ((i < sLength) && (s.charAt(i) != "@"))
    { i++
    }

    if ((i >= sLength) || (s.charAt(i) != "@")) return false;
    else i += 2;

    // look for .
    while ((i < sLength) && (s.charAt(i) != "."))
    { i++
    }

    // there must be at least one character after the .
    if ((i >= sLength - 1) || (s.charAt(i) != ".")) return false;
    else return true;
}





// isYear (STRING s [, BOOLEAN emptyOK])
// 
// isYear returns true if string s is a valid 
// Year number.  Must be 2 or 4 digits only.
// 
// For Year 2000 compliance, you are advised
// to use 4-digit year numbers everywhere.
//
// And yes, this function is not Year 10000 compliant, but 
// because I am giving you 8003 years of advance notice,
// I don't feel very guilty about this ...
//
// For B.C. compliance, write your own function. ;->
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function isYear (s)
{   if (isEmpty(s)) 
       if (isYear.arguments.length == 1) return defaultEmptyOK;
       else return (isYear.arguments[1] == true);
    if (!isNonnegativeInteger(s)) return false;
    return ((s.length == 2) || (s.length == 4));
}



// isIntegerInRange (STRING s, INTEGER a, INTEGER b [, BOOLEAN emptyOK])
// 
// isIntegerInRange returns true if string s is an integer 
// within the range of integer arguments a and b, inclusive.
// 
// For explanation of optional argument emptyOK,
// see comments of function isInteger.


function isIntegerInRange (s, a, b)
{   if (isEmpty(s)) 
       if (isIntegerInRange.arguments.length == 1) return defaultEmptyOK;
       else return (isIntegerInRange.arguments[1] == true);

    // Catch non-integer strings to avoid creating a NaN below,
    // which isn't available on JavaScript 1.0 for Windows.
    if (!isInteger(s, false)) return false;

    // Now, explicitly change the type to integer via parseInt
    // so that the comparison code below will work both on 
    // JavaScript 1.2 (which typechecks in equality comparisons)
    // and JavaScript 1.1 and before (which doesn't).
    var num = parseInt (s);
    return ((num >= a) && (num <= b));
}



// isMonth (STRING s [, BOOLEAN emptyOK])
// 
// isMonth returns true if string s is a valid 
// month number between 1 and 12.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function isMonth (s)
{   if (isEmpty(s)) 
       if (isMonth.arguments.length == 1) return defaultEmptyOK;
       else return (isMonth.arguments[1] == true);
    return isIntegerInRange (s, 1, 12);
}



// isDay (STRING s [, BOOLEAN emptyOK])
// 
// isDay returns true if string s is a valid 
// day number between 1 and 31.
// 
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function isDay (s)
{   if (isEmpty(s)) 
       if (isDay.arguments.length == 1) return defaultEmptyOK;
       else return (isDay.arguments[1] == true);   
    return isIntegerInRange (s, 1, 31);
}



// daysInFebruary (INTEGER year)
// 
// Given integer argument year,
// returns number of days in February of that year.

function daysInFebruary (year)
{   // February has 29 days in any year evenly divisible by four,
    // EXCEPT for centurial years which are not also divisible by 400.
    return (  ((year % 4 == 0) && ( (!(year % 100 == 0)) || (year % 400 == 0) ) ) ? 29 : 28 );
}



// isDate (STRING year, STRING month, STRING day)
//
// isDate returns true if string arguments year, month, and day 
// form a valid date.
// 

function isDate (year, month, day)
{   // catch invalid years (not 2- or 4-digit) and invalid months and days.
    if (! (isYear(year, false) && isMonth(month, false) && isDay(day, false))) return false;

    // Explicitly change type to integer to make code work in both
    // JavaScript 1.1 and JavaScript 1.2.
    var intYear = parseInt(year);
    var intMonth = parseInt(month);
    var intDay = parseInt(day);

    // catch invalid days, except for February
    if (intDay > daysInMonth[intMonth]) return false; 

    if ((intMonth == 2) && (intDay > daysInFebruary(intYear))) return false;

    return true;
}




/* FUNCTIONS TO NOTIFY USER OF INPUT REQUIREMENTS OR MISTAKES. */


// Display prompt string s in status bar.

function prompt (s)
{   window.status = s
}



// Display data entry prompt string s in status bar.

function promptEntry (s)
{   window.status = pEntryPrompt + s
}




// Notify user that required field theField is empty.
// String s describes expected contents of theField.value.
// Put focus in theField and return false.

function warnEmpty (theField, s)
{   theField.focus()
    alert(mPrefix + s + mSuffix)
    return false
}



// Notify user that contents of field theField are invalid.
// String s describes expected contents of theField.value.
// Put select theField, pu focus in it, and return false.

function warnInvalid (theField, s)
{   theField.focus()
    theField.select()
    alert(s)
    return false
}




/* FUNCTIONS TO INTERACTIVELY CHECK VARIOUS FIELDS. */

// checkString (TEXTFIELD theField, STRING s, [, BOOLEAN emptyOK==false])
//
// Check that string theField.value is not all whitespace.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkString (theField, s, emptyOK)
{   // Next line is needed on NN3 to avoid "undefined is not a number" error
    // in equality comparison below.
    if (checkString.arguments.length == 2) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    if (isWhitespace(theField.value)) 
       return warnEmpty (theField, s);
    else return true;
}



// checkStateCode (TEXTFIELD theField [, BOOLEAN emptyOK==false])
//
// Check that string theField.value is a valid U.S. state code.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkStateCode (theField, emptyOK)
{   if (checkStateCode.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    else
    {  theField.value = theField.value.toUpperCase();
       if (!isStateCode(theField.value, false)) 
          return warnInvalid (theField, iStateCode);
       else return true;
    }
}



// takes ZIPString, a string of 5 or 9 digits;
// if 9 digits, inserts separator hyphen

function reformatZIPCode (ZIPString)
{   if (ZIPString.length == 5) return ZIPString;
    else return (reformat (ZIPString, "", 5, "-", 4));
}




// checkZIPCode (TEXTFIELD theField [, BOOLEAN emptyOK==false])
//
// Check that string theField.value is a valid ZIP code.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkZIPCode (theField, emptyOK)
{   if (checkZIPCode.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    else
    { var normalizedZIP = stripCharsInBag(theField.value, ZIPCodeDelimiters)
      if (!isZIPCode(normalizedZIP, false)) 
         return warnInvalid (theField, iZIPCode);
      else 
      {  // if you don't want to insert a hyphen, comment next line out
         theField.value = reformatZIPCode(normalizedZIP)
         return true;
      }
    }
}



// takes USPhone, a string of 10 digits
// and reformats as (123) 456-789

function reformatUSPhone (USPhone)
{   return (reformat (USPhone, "(", 3, ") ", 3, "-", 4))
}



// checkUSPhone (TEXTFIELD theField [, BOOLEAN emptyOK==false])
//
// Check that string theField.value is a valid US Phone.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkUSPhone (theField, emptyOK)
{   if (checkUSPhone.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    else
    {  var normalizedPhone = stripCharsInBag(theField.value, phoneNumberDelimiters)
       if (!isUSPhoneNumber(normalizedPhone, false)) 
          return warnInvalid (theField, iUSPhone);
       else 
       {  // if you don't want to reformat as (123) 456-789, comment next line out
          theField.value = reformatUSPhone(normalizedPhone)
          return true;
       }
    }
}



// checkInternationalPhone (TEXTFIELD theField [, BOOLEAN emptyOK==false])
//
// Check that string theField.value is a valid International Phone.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkInternationalPhone (theField, emptyOK)
{   if (checkInternationalPhone.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    else
    {  if (!isInternationalPhoneNumber(theField.value, false)) 
          return warnInvalid (theField, iWorldPhone);
       else return true;
    }
}



// checkEmail (TEXTFIELD theField [, BOOLEAN emptyOK==false])
//
// Check that string theField.value is a valid Email.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkEmail (theField, emptyOK)
{   if (checkEmail.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    else if (!isEmail(theField.value, false)) 
       return warnInvalid (theField, iEmail);
    else return true;
}


// Check that string theField.value is a valid Year.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkYear (theField, emptyOK)
{   if (checkYear.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    if (!isYear(theField.value, false)) 
       return warnInvalid (theField, iYear);
    else return true;
}


// Check that string theField.value is a valid Month.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkMonth (theField, emptyOK)
{   if (checkMonth.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    if (!isMonth(theField.value, false)) 
       return warnInvalid (theField, iMonth);
    else return true;
}


// Check that string theField.value is a valid Day.
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function checkDay (theField, emptyOK)
{   if (checkDay.arguments.length == 1) emptyOK = defaultEmptyOK;
    if ((emptyOK == true) && (isEmpty(theField.value))) return true;
    if (!isDay(theField.value, false)) 
       return warnInvalid (theField, iDay);
    else return true;
}



// checkDate (yearField, monthField, dayField, STRING labelString [, OKtoOmitDay==false])
//
// Check that yearField.value, monthField.value, and dayField.value 
// form a valid date.
//
// If they don't, labelString (the name of the date, like "Birth Date")
// is displayed to tell the user which date field is invalid.
//
// If it is OK for the day field to be empty, set optional argument
// OKtoOmitDay to true.  It defaults to false.

function checkDate (yearField, monthField, dayField, labelString, OKtoOmitDay)
{   // Next line is needed on NN3 to avoid "undefined is not a number" error
    // in equality comparison below.
    if (checkDate.arguments.length == 4) OKtoOmitDay = false;
    if (!isYear(yearField.value)) return warnInvalid (yearField, iYear);
    if (!isMonth(monthField.value)) return warnInvalid (monthField, iMonth);
    if ( (OKtoOmitDay == true) && isEmpty(dayField.value) ) return true;
    else if (!isDay(dayField.value)) 
       return warnInvalid (dayField, iDay);
    if (isDate (yearField.value, monthField.value, dayField.value))
       return true;
    alert (iDatePrefix + labelString + iDateSuffix)
    return false
}