HTML end tag and w3c standard _ HTML/Xhtml _ webpage Creation

Html must end with html, which is a complete element. Unless it is a self-enclosed tag, most websites currently use xhtml standards for seo and multi-browser support based on w3c principles, each start tag in xml must have a corresponding end tag, that is, it must have an end, which is a complete element, unless it is a self-closed tag, self-closed is such a label.
Html is a sub-level of xml, so we must also follow the xml principle. This is the standard.
So, It ends without adding/> and does not conform to the standard. It is only applicable to versions earlier than html 4.0. Currently, most websites use xhtml standard for seo and multi-browser support.