Yepp, you are definitely right.

They just overlay a window over the buffer.

To answer the questions:

* arrow keys move normally through the file as if the overlay window was not there
* arrow keys don't move into the file, nor do they move outside the file once the window get the focus
* arrow keys behave just as normally as they do in a files, the context is switched by pressing with a mouse 
   cursor inside the new buffer (I don't know if there is a command/shortcut to do it without mouse, I don't use 
   brackets - I am just curious about it).
* search is working as if they are separate files; it searches in the buffer with focus
* text selection is also behaving as if they are separate buffers: it continues through buffer below the overlay or not going
   outside of overlay buffer. - also it is not possible to select text across files

Here are some screenshots I took with selection, search and also to show how they display code with same name but in different
files:

http://nextpoint.se/bc/b1.png
http://nextpoint.se/bc/b2.png
http://nextpoint.se/bc/b3.png
http://nextpoint.se/bc/b4.png
http://nextpoint.se/bc/b5.png

Of course, just because Brackets does it one way or another, does not mean Emacs has to do same way.


> Date: Wed, 19 Mar 2014 14:17:58 -0400
> From: rms@gnu.org
> To: arthur.miller@live.com
> CC: emacs-devel@gnu.org
> Subject: Re: "Adobe Brackets like" editing in emacs
> 
> [[[ To any NSA and FBI agents reading my email: please consider    ]]]
> [[[ whether defending the US Constitution against all enemies,     ]]]
> [[[ foreign or domestic, requires you to follow Snowden's example. ]]]
> 
>     Here is a picture of how it looks like: 
> 
>     http://dev.brackets.io/preso/intro/assets/features/brackets-quick-edit-js.PNG
> 
> It appears that this displays a portion of another file in the middle
> of the file you are editing.  Right?
> 
> How do editing commands behave in that situation?
> Does that editor have keyboard editing commands?
> For instance, do arrow keys normally move through the file?
> If so, what do the arrow keys do in that mode?
> Do they move into, through, and out of the portion of the other file?
> If you search in that mode, does it search through the text that is visible?
> 
> What happens if you try to select a region with one end
> inside one file and the other end in another file?
> Can you do that?  If so, what happens if you delete that region?
> 
> 
> -- 
> Dr Richard Stallman
> President, Free Software Foundation
> 51 Franklin St
> Boston MA 02110
> USA
> www.fsf.org  www.gnu.org
> Skype: No way! That's nonfree (freedom-denying) software.
>   Use Ekiga or an ordinary phone call.
>