From Xojo Documentation
| This property is only available on the Windows platform.
For cross-platform compatibility, use ＃If...＃Endif with the Target... specifiers to make sure you will not attempt to use this property on an incompatible platform.
HideSelection hides the selection highlight when the TextArea loses the focus. The default is True.
If HideSelection is False, then the TextArea retains its selection when another field gains the focus. HideSelection is currently a Windows only property.