From Xojo Documentation
| This item was deprecated in version 2019r2.
| This method is only available on the macOS platform.
For cross-platform compatibility, use ＃If...＃Endif with the Target... specifiers to make sure you will not attempt to use this method on an incompatible platform.
Adds NewValue to the end of the array of property values, identified by Label. Append is for managing multi-value properties such as phone numbers, addresses, email addresses, and so forth. See notes on labels in the description of the Insert method.