As part of the Sitecore upgrade from 8.2 to 9.1, I was upgrading dynamic placeholder keys as per Sitecore 9.1 format. For this, I have got below blog which was very helpful.
But in my case placeholder keys with underscore are not working so I have updated few keys and replaced underscore with hyphen and that worked for me. I have seen many other blogs too where people have mentioned "Underscore" in key format.
My question is what is the right format of Sitecore 9 dynamic placeholder key?? Should this have hyphen or underscore?