Yes, it makes sense Burt_Harris. I like the flexibility your proposal would give.
Btw, do you think this could be a metadata? Because maybe we could include it in as part of a document declaration. Or should we still stick with <!CommonMark 0.1.23-github.username.projectname > (or both?)
E.g.
My Title
| !CommonMark: 0.1.23-github.username.projectname
| title: Title for the top bar of any browser
| author: average joe
| layout: resume
.... Content Here ....