In Android Studio, when a project is created it includes a bunch of `drawable` folders, but each with a suffix indicating their size.

For example, there's 

```
drawable-mdpi
drawable-hdpi
drawable-xhdpi
...

```

However, very often I see instructions to add something to the `drawable` folder. For example, in the Android documentation about `selector` xml resources, [here](http://developer.android.com/guide/topics/resources/drawable-resource.html).

Should I add a `drawable` folder without a suffix? Or should I add the xml file to all of the different `drawables`? Why is there no plain `drawable` from the beginning?