Android drawable folders fallback rule

I'm trying to understand how the drawable folders in Android works. I found that in the resource folder in our project, it has the following folders:

res/drawable-ldpi/
res/drawable-ldpi-v8/
res/drawable-ldpi-v11/
res/drawable-mdpi/
res/drawable-mdpi-v8/
res/drawable-mdpi-v11/
res/drawable-hdpi/
res/drawable-hdpi-v8/
res/drawable-hdpi-v11/
res/drawable-xhdpi/
res/drawable-xhdpi-v8/
res/drawable-xhdpi-v11/
res/drawable-xxhdpi/
res/drawable-xxhdpi-v8/
res/drawable-xxhdpi-v11/

Can someone please educate me on how the fallback mechanism on these folders works? Also what does v8 and v11 mean?