//<![CDATA[
function Validate_String(string, return_invalid_chars)
         {
         valid_chars = '1234567890-_.^~abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
         invalid_chars = '';
         
         if(string == null || string == '')
            return(true);
         
         //For every character on the string.   
         for(index = 0; index < string.length; index++)
            {
            char = string.substr(index, 1);                        
            
            //Is it a valid character?
            if(valid_chars.indexOf(char) == -1)
              {
              //If not, is it already on the list of invalid characters?
              if(invalid_chars.indexOf(char) == -1)
                {
                //If it's not, add it.
                if(invalid_chars == '')
                   invalid_chars += char;
                else
                   invalid_chars += ', ' + char;
                }
              }
            }                     
            
         //If the string does not contain invalid characters, the function will return true.
         //If it does, it will either return false or a list of the invalid characters used
         //in the string, depending on the value of the second parameter.
         if(return_invalid_chars == true && invalid_chars != '')
           {
           last_comma = invalid_chars.lastIndexOf(',');
           
           if(last_comma != -1)
              invalid_chars = invalid_chars.substr(0, $last_comma) + 
              ' and ' + invalid_chars.substr(last_comma + 1, invalid_chars.length);
                      
           return(invalid_chars);
           }
         else
           return(invalid_chars == ''); 
         }


function Validate_Email_Address()
         {

         var email_address=document.email.txtemail.value;

         //Assumes that valid email addresses consist of user_name@domain.tld
         at = email_address.indexOf('@');
         dot = email_address.indexOf('.');
     
         if(at == -1 || 
            dot == -1 || 
            dot <= at + 1 ||
            dot == 0 || 
            dot == email_address.length - 1)
            {
            alert('Please enter valid email address.');
            return(false);         		  
			}

         user_name = email_address.substr(0, at);
         domain_name = email_address.substr(at + 1, email_address.length);                  
         
         if(Validate_String(user_name) === false || 
            Validate_String(domain_name) === false)
            {
            alert('Please enter valid email address.');
            return(false);                     
            }
		else
		{	

         return(true);
			}
         }