[Packages can be made into paclets](http://mathematica.stackexchange.com/q/131101/12), which provides easy distribution and versioning. The paclet metadata is in the `PacletInfo.m` file. The settings here also determine how the paclet can extend Mathematica.

What settings and extensions can be used in a `PacletInfo.m` file and what are their effects?

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Related posts:

 * http://mathematica.stackexchange.com/questions/130359/what-is-the-purpose-of-the-kernel-and-application-extensions-in-pacletinfo-m

 * [Create and deploy your own paclets in the Workbench](http://community.wolfram.com/groups/-/m/t/961186)