Firefox UI Guidelines for Voice and Tone.
The style guide itself is good, but what drew my attention was the visual representation of tone ranges. Personally, I find the visual a far more clear example of what the Firefox UI copy should read like than a bullet list of examples would have conveyed. I also appreciate how a range implies flexibility for the writer to approach the language from a few different angles. A good reminder that product design writing isn’t about how it’s written, it’s about how it reads.