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Differences Between XHTML And HTML

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Get Ready For XHTML

XHTML is not very different from the HTML 4.01 standard.

So, bringing your code up to the 4.01 standard is a good start.

Our complete HTML 4.01 reference can help you with that.

In addition, you should start NOW to write your HTML code in lowercase letters, and NEVER skip closing tags (like </p>).


The Most Important Differences:

  • XHTML elements must be properly nested
  • XHTML elements must always be closed
  • XHTML elements must be in lowercase
  • XHTML documents must have one root element

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:

<BODY>
<P>This is a paragraph</P>
</BODY>

This is correct:

<body>
<p>This is a paragraph</p>
</body>


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.

The basic document structure is:

<html>
<head> ... </head>
<body> ... </body>
</html>

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