IMPLEMENTATION DETAIL: Marks this JS native module class as having stored
a loading spec in its IR.
This is true iff the module class was compiled with Scala.js 0.6.13 or
Do not use this annotation yourself.
IMPLEMENTATION DETAIL: Marks concrete members of Scala.js-defined JS
traits, so that they can be identified by the back-end not to emit them.
Internally, such members are known as "optional", in reference to their
primary intended use case: optional fields in configuration objects.