//check the form when submitted and display the error message (if any)
		function check_form()
		{
			if (check_name() && check_email_address() && check_comment() && check_code()){return true;}
			else
			{
				check_name();
				check_email_address();
				check_comment();
				check_code();
				return false;
			}
		}
		
		//reset page layout
		function reset_form()
		{
			var checkName = window.document.getElementById('name_status');
			var checkEmailAddress = window.document.getElementById('email_status');
			var checkComment = window.document.getElementById('comment_status');
			var checkCode = window.document.getElementById('code_status');
			
			checkName.innerHTML = "";
			checkEmailAddress.innerHTML = "";
			checkComment.innerHTML = "";
			checkCode.innerHTML = "&nbsp;&nbsp;<i>Letters are not case-sensitive</i>";
			checkCode.className = "";
		}
		
		//check name's input field
		function check_name()
		{
			var getName = window.document.main.name;
			var checkName = window.document.getElementById('name_status');

   			// if name is empty, alert the visitor
   			if (trim(getName.value) == '')
   			{
				checkName.innerHTML = "please enter your name..";
				checkName.className = "alert";
      			return false;
   			}
			else
			{
				checkName.innerHTML = "";
      			return true;
			}
		}
		
		//check email address's input field
		function check_email_address()
		{
			var getEmailAddress = window.document.main.email_address;
			var checkEmailAddress = window.document.getElementById('email_status');
			
			// if email address is empty, or not on valid format
			if(trim(getEmailAddress.value) == '' || !isEmail(trim(getEmailAddress.value)))
   			{
				checkEmailAddress.innerHTML = "please enter your email address..";
				checkEmailAddress.className = "alert";
      			return false;
   			}
			else 
			{
				checkEmailAddress.innerHTML = "";
				return true;
			}
		}
		
		//check comment's text area
		function check_comment()
		{
			var getComment = window.document.main.comment;
			var checkComment = window.document.getElementById('comment_status');
			
			// if comment is empty
			if(trim(getComment.value) == '')
   			{
				checkComment.innerHTML = "please enter your comment";
				checkComment.className = "alert";
      			return false;
   			}
			else 
			{
				checkComment.innerHTML = "";
      			return true;
			}
		}
		
		//check code's input field
		function check_code()
		{
			var getCode = window.document.main.code;
			var checkCode = window.document.getElementById('code_status');
			
			// if code is empty
			if(trim(getCode.value)== '')
   			{
				checkCode.innerHTML = "&nbsp;&nbsp;the verification code please..";
				checkCode.className = "alert";
				return false;
			}
			else 
			{
				checkCode.innerHTML = "&nbsp;&nbsp;<i>Letters are not case-sensitive</i>";
				checkCode.className = "";
				return true;
			}
		}
		
		
		//strip whitespace from the beginning and end of a string
		function trim(string)
		{
   			return string.replace(/^\s+|\s+$/g,'');
		}

		
   		//check if a string is in valid email format.
		function isEmail(string)
		{
			var regex = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;		
			return regex.test(string);
		}
	
	//javascript validator script taken from www.php-mysql-tutorial.com
	//javascript regular expression script taken from www.freshmango.com