Because of the semantical orientation of HTML5 many HTML tags have been declared a non-conformant (deprecated) in HTML5. These tags are tags which are either redundant or do not transport meaning but only display properties which should rather be done setting CSS properties than HTML tags.
Here’s the list of tags currently removed in HTML5:
|Removed tag||Usage||Alternative HTML tags||Alternative CSS properties|
|<acronym>||acronym or abbreviation for a word||<abbr>|
|<basefont>||default font size for a document||font, font-family, font-size, font-size-adjust, font-stretch, font-style, font-variant, font-weight, @font-face|
|<big>||text font size one size bigger||font-size|
|<center>||center content horizontally within the containing element||text-align|
|<font>||font size, color and face||font, font-family, font-size, font-size-adjust, font-stretch, font-style, font-variant, font-weight, @font-face|
|<frame>||area in which another HTML document can be displayed||<iframe>|
|<frameset>||container for <frame> elements|
|<noframes>||element used when <frame> elements are not supported|
|<strike>||strike-through||<del> or <span>||text-decoration|
|<tt>||display text with monotype font||<code>|
Note that <u> was on the list of deprecated tags for some time but currently has found its way back into the HTML5 specification. <u> makes the contained text underlined. It's never been a good idea to use it since underlined text generally has a different meaning for users of HTML pages: it usually shows that this text is a link which is not the case with the <u> tag. Of course the same can be achieved with CSS, so this tag is not really required and using it for only display purposes doesn't fit the semantical objective of HTML5. This element only got out of the HTML5 non-conformity because there are scenarios in which it does transport a meaning (Chinese proper name mark, text marked incorrect by a spell-checker, indicate family names).