Artcodes are made up of a boundary, regions and blobs. They have a simple hierarchical structure: blobs are inside the regions, regions are inside the boundary. You can draw as much as you like outside of the boundary as long as it doesn’t touch the boundary.
The number of blobs in each region gives the code. The above is 1:1:1:1:2 because it has 5 regions, four with 1 blob and one with 2 blobs.