Syntax

^Syntax
ActionStrictMode :
   LongActionHeader_{(Code=0x89, Size=actionSize)} actionStrictModeBody_{[size: actionSize]}

actionStrictModeBody :
   isStrict PADDING

isStrict :
   UINT8

The field isStrict corresponds to the boolean isStrict != 0.

TODO: Confirm if padding is allowed.

Description

This AVM1 action only serves as a hint that the byte code was compiled using "strict mode". It has no runtime effect.

I assume this corresponds that the program type-checked. This hint was probably envisioned as a signal to improve performance by relying on the compile-time checks and reducing runtime checks, but in practice it did not work out: AS2 type hints are optional so passing a "strict compilation" does not mean much.

I only found references to this action in other parsers (Gnash and Shumway), but wasn't able to generate it myself. I looked for a "strict compilation" in the editors "Macromedia Flash 8" and "Adobe Flash Pro CS6" but couldn't find it.

Abstract AS2

@strictCompilationHint(); // Default: `true`
@strictCompilationHint(true);
@strictCompilationHint(false);

Gnash documentation

Source

Sets strict mode in the compiler.

This is irrelevant for execution, but included for completeness.