TextOutputStream.Open
From Xojo Documentation
Shared Method
Opens the passed file so that text can be added to the end of the file.
Notes
If no file exists at the specified location, one is created. If the file cannot be created or opened for adding, an IOException is raised. Add text by calling Write or WriteLine.
Example
This example adds the text in TextField1 to the text file that was opened by GetOpenFolderItem: