I just joined a team using SP 2016 and I notice that for the current master page, it has an equivalent html page that is a duplicate of the .master file. Both are in sync with each other and reflect the same changes when a change is made to the .html file. I was told that it is created by sharepoint for every master page file and that we should make changes to the .html equivalent. I noticed that on another SharePoint 2016 site in a different environment, none of the master pages have an equivalent .html file. Any ideas why or am I missing something? Also, how do I create this equivalent .html master page file and keep it in sync with the master page?
Thanks for any enlightenment.