Domain name begins with a sequence of 3 segments, where each segment consists of a decimal number optionally preceded by an alpha piece and optionally separated from that piece by “-” or “_”, and the segments are separated from each other by “-”, “_”, or “.”:
*?(+([a-zA-Z])?([-_]))+([0-9])[-_.]?(+([a-zA-Z])?([-_]))+([0-9])[-_.]?(+([a-zA-Z])?([-_]))+([0-9])*

Leftmost component contains 4 or more decimal digits:
*([!.])[0-9]*([!.])[0-9]*([!.])[0-9]*([!.])[0-9]*

Leftmost component contains 3 decimal numbers separated from each other by non-decimal-digit segments:
*([!.])+([0-9])+([!0-9.])+([0-9])+([!0-9.])+([0-9])*

Domain name contains a component exactly matching one of these names, which is neither the leftmost nor either of the two rightmost components:
*.@(cable|cablemodem|cmodem|catv|ppp|dsl|adsl|dynamic|dyn|user|usr|pool|dpool|resnet|rescomp|residential).*.*

Domain name begins with any of these strings:
@(user|usr|adsluser|client|dial|student-|customer|pool|dpool|your-|host[-.])*

Leftmost component of domain name contains any of these strings:
*([!.])@([-_]ipad|cable|cablemodem|cmodem|catv|ppp|dsl|node)*

Leftmost component consists of “pc” or “ip” followed by decimal digits, optionally separated by a “-”:
@(pc|ip)?(-)+([0-9]).*

Leftmost component contains 3 or more dashes:
+([!.])-+([!.])-+([!.])-+([!.])*

Leftmost component consists entirely of decimal digits:
*([0-9]).*

Domain name contains “dhcp” anywhere in it:
*dhcp*

Other tests include:

• Are there more decimal digits than letters in the leftmost component?
• Does the leftmost component of the domain name end with a string of 8 or more hexadecimal digits, of which at least 4 are decimal digits?