What is "Dynamic Global Hostname" in Internet Options? Is it DDNS?

If you have an Airport Extreme or a Time Capsule with updated firmware you will find "Use dynamic global hostname" in: Airport Utility > Internet tab > Internet options. There is literally no Apple provided documenation on this setting within the device's user manual, instructions, or online support. The only documenation you will find are on various blogs and forums such as this one. So, here is a screenshot of the setting and my questions below:

1. I'm assuming that this is where I can setup Dynamic DNS if I have an account with a DDNS provider such as DynDNS or NoIP. Is this correct?

2. If this is where I can setup DDNS, then what should the hostname be? Should it be the hostname I have setup with a DDNS provider, like this: MySite.DDNS.com? Or, should the hostname include my device's actual hostname, like this: TimeCapsule.MySite.DDNS.com?

3. For the "User" and "Password" fields, should this be the account that I have with the DDNS provider? If yes, then what is the format of the username.. is it just my DDNS account username: "MyAccount"? Or, should it be: MyAccount@MySite.DDNS.com?

I'm trying to setup DDNS because I'd like to have remote SSH access to several of my Linux systems on my network and I don't want to configure a DDNS client on the Linux systems if the Time Capsule can do it. This is because my Time Capsule will always be online but my Linux systems are not always online.

Thanks for any help with this setting! It is definitely strange because "Dynamic Global Hostname" is not an "industry standard" term. Typically, it is called "Dynamic DNS" instead. So that's why I'm trying to figure out what this setting really is and if it can help me with my DDNS and remote access needs.