It is "not support", as in it is not a feature you can access by normal methods of using the launcher, nor will the technical support staff offer assistance with setting it up.
I have two accounts since my girlfriend quit playing and I tried to open a second game on the same computer after minimizing the first game to the task bar and opening the shortcut with -launch at the end but it won't open. It doesn't tell you that there's already a copy of D3 running, it just attempts to open and stays on a black screen.
I was going to drop items from one account and pick them up with another but it looks like I'll have to get help from someone who will accept friendship requests from both the battle tags and then wait on me to come and go.
Threats of violence. We take these seriously and will alert the proper authorities.
Posts containing personal information about other players. This includes physical addresses, e-mail addresses, phone numbers, and inappropriate photos and/or videos.
Harassing or discriminatory language. This will not be tolerated.