For a second I thought they are talking about exporting the mockup to an actual Android layout which made me come back and check for that option, only to not find it. They are just talking about serializing the mockup for later reference.

The saving part is actually quite odd :) I get innerHTML (with inline css to position the elements correctly) of the layout where you can insert objects and save it to database.

This is awesome. Maybe, you can store the current elements coordinates to prevent overlapping on top of each other when you click multiple elements at the same time. Not a biggie. Love it.