Good find! For some reason buried two levels deep from the Previews page. I believe you're right that it's silently building a PreviewDevice from the string. Yo

Good find! For some reason buried two levels deep from the Previews page. I believe you're right that it's silently building a PreviewDevice from the string. You can make the PreviewDevice explicit (as shown in the Hacking with Swift code sample), but nice tidbit that you don't have to.