ActionScript 3 :: How To Write Class Over Several Files

So, how do we write a class over several files in action script 3? In C# there's the "partial" keyword. In C++ it's natural (you just "#include ..." all files). In Flex 3, in a component, you add this tag: <mx:Script source="myfile.as"/>.

How do I split the following class into several files;
package package_path {
public class cSplitMeClass {
public function cSplitMeClass() {
} public function doX():void {
// ....
} public function doY():void {
// ....
}}}
For example I want to have the doX() and doY() functions implemented in another ".as" file.