This dropdown menu contains some classic heading and formatting tags that can be applied to the text.
If you want to apply a specific heading tag to a text,you can either select the text or place the cursor inside the text and then choose a heading tag from the Heading tags drop menu in the toolbar. The heading will be set to the entire paragraph which contains the curent selection. If the current paragraph already has a heading tag applied, it will be replaced by the new selected one.