HTML5 does not support tags or new tags, and html5 does not support new tags
1. tags not supported or not supported by HTML5
<Acronym>-- Define the abbreviation of the first letter, which is not supported by html5. Use <abbr> to define the abbreviation. The title attribute can be used to display the complete version of the abbreviation when the mouse pointer moves over the element, this is friendly to browsers and search engines.
<Applet>-- Defines the embedded applet, which is not supported in HTML5. Use the object element label instead.
<B>-- Specifies the bold text. Supported, but according to HTML5 specifications, the <B> label should be used as the final option only when no other suitable labels are more appropriate. To emphasize important text, we recommend that you use the <strong> label. If it is purely for bold text, we recommend that you use the CSS style font-weight: bold to set bold text.
<Basefont>-- Defines the default font family, color, or size of the text on the page, which is only supported by Internet Explorer. Use CSS style sheets instead.
<Center>-- The definition text is centered. HTML 4.01 does not support it, but HTML5 does not. Use CSS style text-align: center to set text center
<Font>-- Defines the font, size, and color of the defined text. HTML 4.01 does not support the use of HTML 5. Use style settings.