#region lets you specify a block of code that you can expand or collapse when using the outlining feature of the Visual Studio Code Editor. For example:
#region MyClass definition public class MyClass { static void Main() { } } #endregion
A #region block must be terminated with a #endregion directive.
A #region block cannot overlap with a #if block. However, a #region block can be nested in a #if block, and a #if block can be nested in a #region block.