The following elements are removed from HTML5:
<acronym> define a abbreviation for lengthy terms; use <abbr> instead.
<applet> define a small java application; use object instead.
<basefont> define a default font size for a document.
<big> define bigger text than normal; however tag <small> was kept.
<center> put text in the center; use css instead.
<dir> define a directory list; use <ul> instead.
<font> define font size and color; use css instead.
<frame> define a sub window; use <iframe> instead.
<frameset> a set of frames; <isindex> ;use <input> instead.
<noframes> a fallback for <frame> <s> define strikethrough text; use <del> instead.
<strike> define strikethrough text; use <del> instead.
<tt> define teletype text; use css instead.
<u> define underlined text ; redefined in HTML5, represents a misspelled word, we recommend avoid using it.
<xmp> define source code text; use <code> or <pre> with escape characters such as < for <.