You can create a global function, or create a public static property on a class (Singleton Pattern for example).
All you need is a simple file in the default folder of your project and from that point on you have globals, these can be variables and functions.
for instance if you have a file called gv.as in your default project path you would declare its content like below
public class gv
public static var CGIUrl:String = ""; //not bindable just sharable
public static var LanguageCode:String="ENG";
public static var LanguageId:int =125;
public static var sessionID:String;
// user interface configuration values
[Bindable] static public var hiColor:uint = 0xD2D3D5; // works when binding to properties..
[Bindable] static public var loColor:uint = 0x0056A5;
[Bindable] static public var gapSize:int = 20;
public static function testObjects(): void
trace("pause to view objects in this module");
at this point you reverence variables as so
myloColor = gv.loColor;
to set the global variable
gv.loColor = 0x00FFFF;
its also very handy for things like skins where you can bind values to skins (hence the hiColor, loColor above), so rather than the complexities of CSS which sometimes just isn't available you can have xml files you load at runtime that are used to set global variables.