Understanding ActionScript and Flash Player
If you compile a SWF file that contains ActionScript 2.0 with publish settings set to Flash Player 6 and ActionScript 1.0, your code functions as long as it does not use ActionScript 2.0 classes. No case sensitivity is involved with the code, only Flash Player. Therefore, if you compile your SWF file with Publish Settings set to Flash Player 7 or 8 and ActionScript 1.0, Flash enforces case sensitivity.
Data type annotations (strict data types) are enforced at compile time for Flash Player 7 and 8 when you have publish settings set to ActionScript 2.0.
ActionScript 2.0 compiles to ActionScript 1.0 bytecode when you publish your applications, so you can target Flash Player 6, 7, or 8 while working with ActionScript 2.0.