HTML-centric front-end development also means web standards. What they have in common is separation of ideas.
1. HTML is the foundation
2. CSS relies on selectors to provide vision;
3. Javascript relies on HTML events to drive behavior;
4. DOM provides API to modify the HTML DOM structure API to call JavaScript;
5. AJAX provides XMLHTTP API to establish communication between the client and server, and it is asynchronous communication;
6. XHTML is HTML refactored with XML. To be more structured;
7. The semantic use of HTML and the micro-format provide data extraction are part of SEO.