Question: Can I add a subdomain as a domain alias to my main domain?  For example:

• main domain: mydomain.com
• alias: subdomain.mydomain.com

In this fashion, both names would point to your main website (mydomain.com).

Answer: Yes.  Please note that the subdomain cannot exist as an actual subdomain AND as an alias.  I.e., do not create an actual subdomain in the Control Panel first, and then try to add it as an alias (you'll get an error that "the subdomain with such name already exists").  Instead, simply use the domain alias feature, and add the subdomain name there directly as an alias.