The System package contains the capabilities, IME, and security classes. These classes deal with client settings that might affect your application in Flash Player. The System class is in the Top Level package.

 capabilitiesThe Capabilities class determines the abilities of the system and player hosting a SWF file, which lets you tailor content for different formats.
 IMEThe IME class lets you directly manipulate the operating system's input method editor (IME) in the Flash Player application that is running on a client computer.
 securityThe class contains methods that specify how SWF files in different domains can communicate with each other.