Runtime Shared Libraries (RSLs)

runtime shared libraries (RSLs) can be individually loaded, cached, and used by multiple applications.

You use RSLs to reduce the size of Flex applications and there by reduce the time required to download the application.

RSLs are SWF files whose code is used as a shared library between different application SWF files.

there are two kinds of RSLs
* signed RSLs - Signed RSLs are libraries that are signed by Adobe and may be stored in the Flash Player Cache, which can be accessed by applications from any domain.
If you are using a signed RSL, the RSL may not have to be downloaded if the RSL is already in the Flash Player Cache. Singed RSLs have a .swz extension
* unsigned RSLs - are normal SWF files and are not loaded into the Flash Player Cache. They rely on browser's cache to keep them from being downloaded.