From Xojo Documentation
| This property has been deprecated since version 2019r1 and should no longer be used.
Please use Uniform Type Identifiers as a replacement.
| This property is only available on the macOS platform.
For cross-platform development, use ＃If...＃Endif with the Target... specifiers to make sure you will not attempt to use this property on an incompatible platform.
For documents, the 4-character code that identifies the application that would be launched and would open the FolderItem if it were opened from the desktop.
Assign the 4-character string to this property. If the FolderItem refers to a directory on macOS, MacCreator returns "MACS". MacCreator is macOS-specific. MacRoman encoding is used.