what's a valid domain name?

[pyh at mail.nsbeta.info]

I  googled and found this: 

    * A domain name can be up to 63 characters long plus a dot plus the 
characters used to identify the top-level domain (i.e "com", "info", "biz", 
etc.
    * Valid characters in a domain name include letters, numbers and 
hyphens "-". The domain name must start and end with a letter or number. 


So, for this domain name of   
"www.xyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxy.com" 
whose size is larger than 64, is not a valid domain name? 

And is there a RFC item for a valid domain name? 

Regards.