Serializing a field

I am serializing either:

References to objects that derive from UnityEngine.Object (a reference to a MonoBehaviour for example) that isn't generic.
Primitive data types (such as int, float, double, bool, or string)
Enum types.
Certain Unity built-in types: Vector2, Vector3, Vector4, Rect, Quaternion, Matrix4x4, Color, Color32, LayerMask, AnimationCurve, Gradient, RectOffset, GUIStyle.