From Xojo Documentation
| This method is only available on the macOS platform.
For cross-platform development, use ＃If...＃Endif with the Target... specifiers to make sure you will not attempt to use this method on an incompatible platform.
Augments the size of the text used to display the HTML page content. You can use ZoomTextIn several times.
The reverse action is achieved with the ZoomTextOut method.
This example is the Action event of a SegmentedControl: