Star Battle technique: confined region
If every remaining cell of a region sits in one row or column, that line's star belongs to the region and all other cells of that line are out.
Regions and lines (rows or columns) constrain each other. Suppose all the cells where a region can still hold a star lie in a single column. Then the region's star is in that column, which means that column's star is used, so every other cell in that column is out.
It also works backwards. If all remaining cells of a column belong to one region, the column's star is that region's star, so the rest of the region's cells outside the column can be crossed out.
How to spot it
Look at the smallest regions and the most crowded lines first. Ask: “if I list where this region's star could go, do they all share a row or column?”
Example
Example from a real Pencilmark puzzle (#6, 5×5). Solver explanation: “All remaining cells of col 5 belong to region 3, so region 3's star is in col 5. Cross out the rest of region 3.”
Combine it with last candidate to unlock the next star.