The HTML behind the formatting of a Google Docs document is an over-complicated mess -- any automated HTML tends to be. It also assumes the same style as the Google Docs layout, with a narrow column ...

In addition to the well-beaten tiny/huge font issues, HTML font tags in the messages no longer work, either. I did a search and no one seems to have mentioned this, so don't kill me if it's already ...

The belief here is that the keywords you use in H2-H6 subheadings are more heavily weighted in Google’s algorithm than words in plain text and that tags are therefore a ranking factor of their own.