Agree. We should either make this change or remove this sentence entirely as I don't believe it adds anything over and above the accessible name required: true and name from: author.

Authoring guidance like this is better in the Authoring Practices (where this is already listed)

I like this change, and I would prefer that the sentence stay in the spec prose for dialog.

I agree that it doesn't specify anything over and above accessible name required: true and name from: author, however it's surprising how many authors just don't get this.

I would almost go one further and add another sentence that says,

If the dialog contains visible content that serves as a description, authors SHOULD use aria-describedby on the dialog element to point to that content.

Come to think of it, it might even be a good idea to have a sentence pointing out aria-modal, because it is buried in the list of inherited properties and there's no indication in the prose that it just might be really important... perhaps something like:

If the dialog is modal, then authors MUST set the dialog's aria-modal to true.

I'm a bit wary of those additional suggestions @carmacleod. IMO those definitely belong over in the guidance, as I can think of situations where I very well wouldn't agree to either of those.

I can think of situations where I very well wouldn't agree to either of those.

Oh! ... what are the situations?

This PR is good to go.
+1

I'll open another issue to consider adding more about aria-describedby and aria-modal to the dialog prose. :)