Ubuntu – Must apps submitted to the Software Center run from the /opt directory

application-developmentapplication-submissionfilesystempackaging

I read this question, but I'm more confused yet.

In developer.ubuntu.com/showdown I read: "(2) run out of /opt" (I understand "run out" is not in /opt Am I wrong?)
In https://wiki.ubuntu.com/AppReviewBoard/Review/Guidelines#Packaging I read: "our package should install most files in /opt/extras.ubuntu.com/"

It's not clear for me if the app must be in the /opt or out /opt :$

Then, can I use the /usr? Will be the app rejected if it's on /usr?

You may be confused by the language; they all mean the same, ie:

"run out of" == "run in" == "installed in" (all in /opt)

The standard files in /usr/share/doc/<packagename> are permitted, such as copyright, changelog, and examples.
The .desktop file is installed in the standard location /usr/share/applications, but must have the prefix extras- added to its name. Example: extras-foobar.desktop for a package named foobar.
Lenses and scopes are installed in the standard locations, but must have the prefix extras- added to their names. Example: extras-unity-lens-foobar.lens for a package named unity-lens-foobar.