Percentage allows you to display decimal numbers as a percentage.
Start with an attribute in decimal format.
When you are setting the type to Percentage, you can also set additional properties: rounding and minimum and maximum constraint.
If you attempt to enter value which doesn't respect the constraint, it will be marked in red and you won't be able to proceed (row 1). Existing values (which were entered before the constraint was created) that don't respect the constraint (row 2) are highlighted as invalid.