@babel/plugin-transform-runtime and corejs option

[thernstig]

Caveat: I have just recently been learning everything babel, but I've read up extensively, yet it is still possible I misunderstand something.

According to https://babeljs.io/docs/en/babel-plugin-transform-runtime#corejs and this text:

By default, @babel/plugin-transform-runtime doesn't polyfill proposals. If you are using corejs: 3, you can opt into this by enabling using the proposals: true option.

It makes it sound like the package will actually polyfill non proposals. I assume that is incorrect? @babel/plugin-transform-runtime never inserts any polyfills. It just adds imports for helper functions. And in addition when the corejs option is used, it is unclear what it does for me. It sounds like it re-writes helpers, but since the intention of @babel/plugin-transform-runtime is to actually add imports for helpers, then how can it re-write them?

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