samba - Oct 2004 - domain name syntax

Dear Sirs,

where can I find information on domain name restrictions ?
I only know that domain name cannot be more than 11 characters.

1) can it contain special characters < > & (&lt; &gt;
&amp;) which have
special meaning within XML ?

2) can it contain national characters ? UTF ? non-UTF ?

maybe there's regular expression which validates domain name ?

Cheers,
Ilia Chipitsine