I have inherited an old Xojo project with this attribute, which is deprecated (FolderItem.MacCreator )
The code is simply
f.MacCreator = ""
What was the purpose of this library? Is there older xojo documentation in existence which may explain it?
Finally, is there a suggested replacement?
setting it to empty is non-sense. You may just remove that line.
MacCreator used to be a 4 character code to tell which app made a file.
This is in a Save As partcode: the saved file must have an Extension and add it to its name. Check the Open code and match t with the Fie Extension.
The old documentation is not available from Xojo servers (you can ask for the old pdf); a search in the internet certainly will gives you link(s) to download it.
MacCreator has been obsolete for many years. You can simple delete that line of code. Not that assigning an empty string had ever made any sense as the creator code was strictly 4 bytes.