Compiler warning messages identify code that is valid and compiles successfully, but may not be what the author intended. To enable detecting these possible problems, compile ActionScript projects in warning mode.

Some of these warnings (for example, "Missing type declaration.") are coding style choices that you have the option whether to enforce. Others (for example, "Impossible assignment to null.") point out statements that are valid, but are unlikely to behave as the user expects. A third class of warnings covers issues you may encounter when porting ActionScript 2.0 code to ActionScript 3.0.

	Code	Message	Description