function checa(input,requiredFields,fieldNames)
{
    var fieldCheck   = true;
    var fieldsNeeded = "\nSe requiere que proporcione la siguiente información\n\n\t";
    for(var fieldNum=0; fieldNum < requiredFields.length; fieldNum++) {
        if ((input.elements[requiredFields[fieldNum]].value == "") ||
            (input.elements[requiredFields[fieldNum]].value == " ")) {
            fieldsNeeded += fieldNames[fieldNum] + "\n\t";
            fieldCheck = false;
        }
		}

    // ALL REQUIRED FIELDS HAVE BEEN ENTERED
    if (fieldCheck == true)
    {
        return true;
    }
    // SOME REQUIRED FIELDS ARE MISSING VALUES
    else
    {
        alert(fieldsNeeded);
        return false;
    }
}

// CHECK STRING - ENSURE ALL CHARACTERS ARE LETTERS
function toAlpha(checkString)
{
    newString = "";    // REVISED/CORRECTED STRING
    count = 0;         // COUNTER FOR LOOPING THROUGH STRING

    // LOOP THROUGH STRING CHARACTER BY CHARACTER
    for (i = 0; i < checkString.length; i++) {
        ch = checkString.substring(i, i+1);

        // ENSURE CHARACTER IS AN ALPHA CHARACTER
        if ((ch >= "a" && ch <= "z") || (ch >= "A" && ch <= "Z" )) {
            newString += ch;
        }
    }

    return newString;
}