Flash CS4 Professional.
fl.sourcePath
Property; a string that contains a list of items in the global ActionScript 3.0 Source path, which specifies the location of ActionScript class files. Items in the string are delimited by semi-colons. In the authoring tool, the items are specified by choosing Edit > Preferences > ActionScript > ActionScript 3.0 Settings.
The following example adds the /Classes folder to the global ActionScript 3.0 Source path:
fl.trace(fl.sourcePath);
fl.sourcePath = "/Classes;" + fl.sourcePath;
fl.trace(fl.sourcePath);fl.flexSDKPath, fl.externalLibraryPath, fl.libraryPath, document.sourcePath