#include <GGUI/Public/UIWidgetTraits.h>
template<typename T>
GGFieldTraits struct
How a type is a property. Defined for each type a property can have; not otherwise, so a field of a type with no traits doesn't compile when its widget is registered.
A definition has Kind (a GGPropKind), Choices() (the words of a Choice; empty otherwise), Read(value, out, why), and Write(value). Numbers, bool, std::string, GGSize, GGEdges, GGColor, and the layout enums have one.