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 ...

Google has made a minor update to the meta tags and attributes that Google supports help documentation and added the two tags Google does not support. Those include the meta keywords tag and HTML tag ...

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.