Why do the Android docs say intent extras need package prefix

According to the Android docs Intent extra name must have a package prefix. I've been using Intent extra names without prefixes for a long time and it seems like there is no chance of collision since what really matters is the Intent action being unique. So are the docs just wrong or am I missing something?

The docs for putExtra say:

Add extended data to the intent. The name must include a package prefix, for example the app com.android.contacts would use names like "com.android.contacts.ShowAll".