Why react package has coffeescript dependency?

I just created clean meteor app and added react there meteor add react. Together with other packages I got coffeescript. Why?

$ meteor add react

Changes to your project's package version selections:

coffeescript        added, version 1.0.9
cosmos:browserify   added, version 0.4.0
jsx                 added, version 0.2.1
react               added, version 0.1.13
react-meteor-data   added, version 0.1.9
react-runtime       added, version 0.13.3_7
react-runtime-dev   added, version 0.13.3_7
react-runtime-prod  added, version 0.13.3_6

That’s because of the cosmos:browserify and it’s written using coffee.

This doesn’t actually affect your app directly since it’s an internal dependency of an internal dependency of the react package.

OK, got it. Thanks for answers.