For maximum compatibility you might target an old MinSDK version and link against a similarly old android.jar. As a developer, other than during specific testing, you will probably be working on a device with a more up-to-date Android version.
When debugging with Android platform source provided by the Android Source Plugin, the platform version of the source picked up by the plugin will be the same as the version the app is built against, not the version running on the device. Often this works out okay where the source hasn't changed, so it is easy to not worry about it, but sometimes it does matter.
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