In the Browsing tab of the Preferences window (app version 0.99.115.2-beta), there are checkboxes that label keyboard shortcuts "⌘-Z" and "⌘-0 / ⌘-9" There should be no dashes or hyphens in these shortcuts -- just ⌘Z, ⌘0, ⌘9.
Safari has dashes too. Haven't checked HIG.
I've looked, and I'm not sure the HIG or the Apple Style Guide spell this out directly anymore, but they used to. But you can see from Apple's own examples that the basic rule is to use hyphens when spelling out modifier key names, but not to use hyphens when using glyphs to represent the modifier keys. So one would write Shift-Command-N or ⇧⌘N.
Style Guide: https://help.apple.com/applestyleguide/#/apsgf9067ae8?sub=apd5ad237653dc24
gruber We've been lazy here and took that what Safari is doing for granted. Thanks for taking time to dig deeper.