The official IRS refund site has a sa.www4 prefix (sa.www4.irs.gov)

Can anyone tell me what the sa.www4 part is and how it's different from a standard www.? Never seen that before

Just an old naming subdomain convention for related websites.

it means to add 4 more w's....duh

Www is just a subdomain, so is this :p

now I wonder how many subdomains can be added to a domain?
http:///www.ww.w.sub1.sub2.sub3.sub... would be a lovely addition to the internet

@mghrist infinite.

@mghrist as long as the full domain + subdomains length is less then 255 characters, you can go as deep as you like, not sure you'll have a reason to go to such lengths though.

Sub1.a.b.c.d.e.a.whole.bunch.more.example.com

There is 1 limitation though, you.cant.do.do.this.example.com

Where two subdomain next to each other are the same. (Brothers)

https://tools.ietf.org/html/...

@stop

No