From Xojo Documentation
A 'wide' character string. This is primarily used with declares on Windows.
You can assign a standard String to a WString and it will be converted and terminated automatically.
WString implicitly converts to String when assigned to a String variable.
On Windows, a wide character string means 2 bytes per character. The WString data type is typically used to map wchar_t* from OS API calls. To map wchar_t**, use ByRef WString.
On macOS and Linux, it means 4 bytes per character.