Dropdown list like in Gmail address box

[seaport]

I am using Gmail and like the way that Gmail shows the dropdown list of email addresses for me to select. The list refreshes as I type. It is not a real dropdown list form field but rather like a layered menu.

I think this feature is implemented by javascript. But I cannot figure it out by looking at the page source code. Is this some kind of proprietary technology owned by google? If it is not, could someone tell me how it works?

Thanks in advance.

Seaport