Inside Macintosh: AppleScript Scripting Additions Guide /

Chapter 3 - Writing Scripting Additions

Using Other Resources With Scripting Additions

The scripting addition loading mechanism adds the invoked scripting addition's resource file to the top of the target application's resource chain.
This guarantees that resources in the scripting addition's resource file will
be found before resources with the same name or ID in the application or system resource files. For example, in the following script, the resource chain is: Beep scripting addition -> MyApplication -> System file (assuming MyApplication hasn't added anything else to the chain).

tell application "MyApplication"   beep 3
end tell

If a scripting addition is called outside of a Tell statement, the resource chain is the same as just described, except that the application is the application running the script (for example, Script Editor).