Regions that fill rows and columns
Expert technique
What happens when regions are trapped inside a few rows?
If two regions lie entirely inside two rows, their four stars are all four stars those rows can hold. Every other tile in those rows is ruled out. The same works for columns, for one region in one row, and for three in three.
It also runs the other way: if two rows are covered entirely by two regions, those regions spend all their stars in those rows, so the parts of them outside the rows are ruled out. Count regions against rows along each edge of the board first, where regions are most often trapped.