Xojo.IO.FolderItem.IsWriteable
From Xojo Documentation
Method
This is True when you have permissions to write to the file or folder. In the case of a folder, it means you can create files in the folder.
Notes
Even if IsWriteable is True, an attempt to write may fail for other reasons, such as coding errors or insufficient disk space. For example, a write may fail because disk space runs out midway through the write operation. IsWriteable is not intended to check for these type of conditions. If you intend to write to a file, you should attempt to do so and handle any exceptions that may occur.