What is the function of the ASO protection circuit (Area of Safety Operation: ASO) of the three-terminal regulator?

LDO Linear Regulators

Transistors (semiconductors) have a specification item called the Area of Safety Operation. The Area of Safety Operation is the minimum power area that can be used without destroying or deteriorating the transistor. When the potential difference between input and output of the 3-terminal series regulator becomes large, the Area of Safety Operation protection function limits the output current.

The operation of protection circuit characteristics is shown as an example in the datasheets of NJM7800 series and NJM7900 series.
An example of the characteristics is shown in Fig. 1.
The ASO protection circuit may operate simultaneously with the overcurrent protection circuit.