A reference to this instance after the append operation has completed.
The StringBuilder.Append(string) method modifies the existing instance of this class; it does not return a new class instance. Because of this, you can call a method or property on the existing reference and you do not have to assign the return value to a System.Text.StringBuilder object, as the following example illustrates.
code reference: System.Text.StringBuilder.Append#2
If value is null, no changes are made.
The capacity of this instance is adjusted as needed.