Canvas height options & ldquo; Auto-resize & rdquo; vs & ldquo; Fluid & rdquo; in the application settings


A question about Canvas Height setting in the Facebook Settings.
There are 2 options Auto-Resize and Fluid and they seem to function in the same way.
In the Canvas Tutorial, it seems that the 2nd option should be scroll bars for Canvas Height, so I'm assuming that Fluid option is a new feature.

But what is the difference between Canvas Height set to Auto-Resize or Fluid?

Here is the documentation