There have been a few posts here asking about how to create accidentals with square brackets, to denote editorial markings. I’ve found out how you can do it! In the Key Signature panel, under “Tonality System”, click on the pencil icon to edit the Tonality system.
Here, you can then add a new accidental with the Plus icon.
In the next dialog, add each of the symbols from the options on the right hand side. You can then select them using the “Previous” “Next” buttons. You’ll have to adjust the position of the brackets using the X and Y values below, and annoyingly, all the chars that were added after the current one inherit its values. You’ll get the hang of it.
Don’t forget to add a value for pitch delta in the top right. Sharp +1, Flat -1. Natural 0.
You can then save this modified tonality as a default, and so it will be available in all new documents! I haven’t found a way of adding it to existing documents without doing it from scratch.
All credit for this tip goes to Jawher Matmati on the Dorico FaceBook group. But it’s such a great tip and really opens up what I can do with Dorico.