This guide is also completely from w3 schools
XHTML Elements Must Be Properly Nested
In HTML, some elements can be improperly nested within each other, like this:
<b><i>This text is bold and italic</b></i>
In XHTML, all elements must be properly nested within each other, like this:
<b><i>This text is bold and italic</i></b>
Note: A common mistake with nested lists, is to forget that the inside list must be within <li> and </li> tags.
This is wrong:
<ul>
<li>Coffee</li>
<li>Tea
<ul>
<li>Black tea</li>
<li>Green tea</li>
</ul>
<li>Milk</li>
</ul>
This is correct:
<ul>
<li>Coffee</li>
<li>Tea
<ul>
<li>Black tea</li>
<li>Green tea</li>
</ul>
</li>
<li>Milk</li>
</ul>
Notice that we have inserted a </li> tag after the </ul> tag in the "correct" code example.
XHTML Elements Must Always Be Closed
Non-empty elements must have a closing tag.
This is wrong:
<p>This is a paragraph
<p>This is another paragraph
This is correct:
<p>This is a paragraph</p>
<p>This is another paragraph</p>
Empty Elements Must Also Be Closed
Empty elements must also be closed.
This is wrong:
A break: <br>
A horizontal rule: <hr>
An image: <img src="happy.gif" alt="Happy face">
This is correct:
A break: <br />
A horizontal rule: <hr />
An image: <img src="happy.gif" alt="Happy face" />
XHTML Elements Must Be In Lower Case
Tag names and attributes must be in lower case.
This is wrong:
[CODE]]<BODY>
<P>This is a paragraph</P>
</BODY>
This is correct:
<body>
<p>This is a paragraph</p>
</body>[/CODE
XHTML Documents Must Have One Root Element
All XHTML elements must be nested within the <html> root element. Child elements must be in pairs and correctly nested within their parent element.
Originally Posted by ___GodLike___
