Known JavaScript Directives [duplicate]

Question

The ECMAScript specification defines the Use Strict Directive, but permits implementations to define their own directives. From here:

Implementations may define implementation specific meanings for ExpressionStatement productions which are not a Use Strict Directive and which occur in a Directive Prologue.

What are the known implementation-specific directives? A quick Google search yields nothing other than use strict.

I can think of use asm and use strong. Are there any others in use?

Answer 1

For Spidermonkey I found only source:

macro(useAsm, useAsm, "use asm")
macro(useStrict, useStrict, "use strict")

V8 same source:

F(use_asm, "use asm")                            
F(use_strict, "use strict")