Tags and Attributes Deprecated in HTML 5
The following elements and attributes have been deprecated and therefore should not be used in HTML documents.
<a name>
or<a id>
withouthref
<acronym>
tag<applet>
tag<bgsound>
tag- the
marginheight
andmarginwidth
attributes of the <body> tag <center>
tag<dir>
tag<fn>
footnote tag<font>
and<basefont>
tags<frameset>
,<frame>
and<noframes>
tags- the
align
,border
,controls
,dynsrc
,hspace
,loop
,start
andvspace
attributes of the <img> tag - inline style tags:
<big>
,<blink>
,<strike>
,<tt>
and<u>
<isindex>
tag<layer>
,<ilayer>
and<nolayer>
tags<listing>
tag<marquee>
tag<nobr>
tag<noembed>
tag<noscript>
tag<onreset>
event attribute<plaintext>
tag- the
language
attribute of the <script> tag <spacer>
tag<xml>
tag<xmp>
tag
Other things to avoid in HTML
Here are some other things that should be avoided when coding HTML documents:
- The named non-breaking space HTML entity
should be avoided. The decimal entity 
or hexadecimal 
should be used instead. - The character sequence
]]>
should be avoided unless it indicates the end of a CDATA section.