Updated: 2013-01-20
Characters not available on the keyboard can be entered using their Unicode code points (here, hexadecimal). Entering these characters directly into documents is prefered over using (X)HTML character references (�
).
Create HTML 5 (markup, HTML 4 differences) documents that can be both HTML and XML (XHTML). See the W3C's Polyglot Markup: HTML-Compatible XHTML Documents. Not complete, just select reminders.
<!DOCTYPE html>
<html lang="en-US" xml:lang="en-US" xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="UTF-8"/>
<title></title>
</head>
<body></body>
</html>
br
) are <element/>
(an not <element>
or <element></element>
), other empty elements (eg p
) are <element></element>
(not <element/>
)<link rel="" href=""/>
and <script src=""></script>
)tr
s in a tbody
, thead
, or tfoot
, and col
s in a colgroup
<pre>
or <textarea>


)lang
and xml:lang
noscript
When you feel like including metadata… just add the attributes (lite (or core)) to the document (unlike earlier).
Check out schema.org for vocabulary.