When declaring a feature, you can add an <ActivationDependencies> section in your feature.xml. Here you can list the features your feature is depending on.
According to the documentation on activation dependencies (http://msdn.microsoft.com/en-us/library/aa543162.aspx), the dependant features get automatically activated if they are in the same scope: If a Feature is dependent on another Feature at the same scope, and the second Feature is not activated when the first one is activated, Windows SharePoint Services activates the second Feature.”
This is incorrect.
The second feature is activated automatically only if it is hidden!