In the "Working with SwiftUI's public interface" section of the Preface, there are instructions to enter a command.

• enter the command in the Terminal application.
• note that all the text, starting with "xed" and continuing to the end "simulator.swiftinterface" is all one command. (On my laptop it inserted a line break after "xed".)
• note that there is a space near the beginning of the command, after "xed" and before "/Applications".
• finally, note that if you copy and paste the text straight into Terminal, some extraneous text will be generated. I pasted into TextEdit, cleaned up the pasted code there, then copied that into Terminal.

Thanks very much @pitman, spot-on and very useful!

I hit an additional bump in the road...

Using Xcode Beta, the commands need to be converted to allow for Beta:

sudo xcode-select -s /Applications/Xcode-beta.app

xed /Applications/Xcode-beta.app/Contents/...

I hope this helps anyone with the same issue...