What ia allowed in the making up of a domain name

[Callme]

Hi
Which of the following symbols is allowed in making up a Domain name ?
Dashes -
Underscores _
Slashes /
Dots .
Also whch extensions are allowed in a Domain name ?
.com
.net
.ca etc.
Thanks

[megri]

You can use only Dashes - in domain name and it can have all extension .com
.net
.ca

[grom]

You can use only Dashes - in domain name and it can have all extension .com
.net
.ca
That would look strange IMO.

[asolls]

I know that hyphens are allowed.
Dots may be used in subdomains.
I think that all extensions are allowed in domain name.

[Skynex53]

good very good !