public static bool wideMode { get; set; }

Wide mode is a mode for Editor GUI where the controls for structs such as Vector3 and Rect are inlined so they take up less vertical space. For example, in wide mode a Vector3Field takes up one line height instead of two, and a RectField takes up two line heights instead of three.

When creating your own multi-line controls, you can query wideMode and make the layout of your control follow the same logic.