There are a lot of posts asking if it's okay to mix commas and dashes like this:
I walked my dog – who is nice, around the neighborhood.
And that's definitely not correct.
But what about the case of using the dash and comma simultaneously?
Which of these is correct?
I walked my dog, Frank – who is nice, around the neighborhood.
I walked my dog, Frank – who is nice – around the neighborhood.
The sentence contains incidental information within incidental information. An appositive within an appositive. This is equivalent to:
I walked my dog [Frank (who is nice)] around the neighborhood.
However, when using dashes and commas, I've read I can't do this:
I walked my dog, Frank – who is nice –, around the neighborhood.
So, I have to close two, "brackets," with one punctuation mark: a dash or a comma.
The lack of a "closing" dash troubles me just as much as the lack of a "closing" comma.