1 min lesson
When the selection is too broad
Use the lesson to respond to this: "The edit looks plausible. Which warning sign do you check first?" Keep the answer plain.
Step 1 of 3
A plausible suggestion can still hide this problem: Selecting an entire file for a four-line change.
Interactive diagram. Tab through its regions; each focused region shows its detail in the panel below.
diagram: compare
Pick a row to see what to look for.