Which of the following are NOT types of 'headlines?'

Social snippets are not a type of headline; they are the preview text and images displayed when content is shared on social media platforms. While they contain a headline (often pulled from the article's title tag or H1), the snippet itself encompasses more than just the headline. Article H1 headers are the main, most important headline on a webpage, typically defining the page's primary topic. Title tags are HTML elements that specify the title of a webpage, appearing in browser tabs and search engine results as the main headline. Email subject lines are the short, descriptive text displayed in an email inbox, serving as the headline for the email's content. All three of these directly function as headlines for their respective content types.