Question

Please explain me what is a framework RSL and difference between Signed and un-signed framework RSLs in Flex. Thank you in advance.

Answer 1

First, there is a wonderful tool called “search” on this website which could have also pointed you in the right direction.

For example:
Flex RSL Understanding
using framework RSL to reduce SWF filesize

Then after googling for “unsigned rsl”, you take the first entry being an official Adobe LiveDoc

There it clearly states:

Every Flex application uses some aspects of the Flex framework, which
is a relatively large set of ActionScript classes that define the
infrastructure of a Flex application. If a client loads two different
Flex applications, the application will likely load overlapping class
definitions. This can be a problem for users who are on dialup or slow
network connections. It also leads to the perception that Flex
applications load more slowly than HTML-based applications.

To overcome these limitations, you can use framework RSLs with your
Flex applications. These libraries are comprised of the Flex class
libraries and can be used with any Flex application. Framework RSLs
come in two versions: signed and unsigned. Signed framework RSLs are
cached in a special Player cache rather than the browser cache. They
can be accessed by any application regardless of that application’s
originating domain. They only need to be downloaded to the client
once, and they are not cleared from the client’s disk when the
browser’s cache is cleared. Unsigned framework RSLs are cached in the
browser cache and can only be used by applications that have access to
the RSL’s domain.

Flash Player 9.0.115 and later support loading signed framework RSLs.
These RSLs can be loaded by applications in different domains. The
framework RSLs are signed and have the extension SWZ. Only Adobe can
create signed RSLs, and only signed RSLs can be stored in the Player
cache. If you create an RSL that contains a custom library, it will be
unsigned. You cannot sign it. If a Player with a version earlier than
9.0.115 attempts to load a framework RSL, then Flash Player skips it and loads a failover RSL, if one was specified when the application
was compiled.

Cheers