HTML code is always accompanied by its “boilerplate” of tags. The very first tag found on any HTML file must be a Doctype declaration.
The html5 doctype
<!DOCTYPE html> is a required preamble used to inform the browser which rendering mode to use (HTML5 vs. XHTML). Be sure to place the doctype at the very top of the document.
<html> <head> <meta charset=UTF-8> <title>Document Title</title> </head> <body> <p>Document content.</p> </body> </html>