I've looked through the Xamarin help pages, and might have missed something. As I cannot seem to find any explanation of what the padding numbers are. Here for example:
<StackLayout Padding="20,0,0,0">
<StackLayout Padding="20,10,0,0">
<StackLayout Padding="20,0">
What is the 1st, 2nd, 3rd and 4th and what happens when I just specify two padding numbers?