The Host Is() inquiry function identifies the current operating system. Then actions specific to that operating system can be performed.
The following example specifies text sizes in reports for different operating systems. If you commonly write your scripts on Windows and share them with macOS users, the results can look different from what you intended. For example, the following expression sets the text to a larger size (12) on macOS and a smaller size (10) on Windows:
textsize = If( Host is( "Mac" ), 12, 10 );