What does the 'configurable' property flag control?
The 'configurable' property flag controls two important aspects: 1) Whether the property can be deleted from the object, 2) Whether the property's descriptor can be changed after creation, 3) When false, attempts to delete the property or modify its descriptor will fail, 4) A non-configurable property's descriptor can't be changed except for writable→false (one-way change), 5) It prevents property redefinition via Object.defineProperty(), 6) It's essential for creating truly permanent object characteristics, 7) Built-in objects often use this to protect critical properties and methods.