What does the [Flags] Enum Attribute mean in C#?

Question

From time to time I see an enum like the following:

[Flags]
public enum Options 
{
    None    = 0,
    Option1 = 1,
    Option2 = 2,
    Option3 = 4,
    Op         


        

Answer 1

To add Mode.Write:

Mode = Mode | Mode.Write;