The experimental object contains features that are known to have unstable API or behavior that may change in future releases.
Experimental features may undergo API changes in future releases, so production code should not rely on them.
Programmers are encouraged to try out experimental features and report any bugs or API inconsistencies they encounter so they can be improved in future releases.
Only where this feature is enabled, are macro definitions allowed.
macros is not enabled, macro definitions are rejected by the compiler.
Macro implementations and macro applications are not governed by this language feature; they can be used anywhere.
Why introduce the feature? Macros promise to make the language more regular, replacing ad-hoc language constructs with a general powerful abstraction capability that can express them. Macros are also a more disciplined and powerful replacement for compiler plugins.
Why control it? For their very power, macros can lead to code that is hard to debug and understand.