The Inner Limits was invented by the Japanese puzzle company
Nikoli (under the name Bag, although the name Corral is probably more well-known amongst the global puzzle community).
1. Draw a single loop along the grid lines. The loop may not cross itself or branch off. In other words, the interior of the loop will be a single polygon.
2. Every number must be contained inside the loop.
3. A number indicates how many grid cells, including the cell itself, lie in an uninterrupted horizontal or vertical line from that cell, up to the nearest edges of the loop.