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Differences Between XHTML and HTML

You can prepare yourself for XHTML by starting to write strict HTML.

How to Get Ready for XHTML

XHTML is the next generation of HTML, but it will of course take some time before browsers and other software products are ready for it.

In the meantime there are some important things you can do to prepare yourself for it. As you will learn from this tutorial, XHTML is not very different from HTML 4.01, so bringing your code up to 4.01 standards is a very 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 make the bad habit of skipping end tags like the </p>.

Happy coding!

The Most Important Differences:

XHTML elements must be properly nested
XHTML documents must be well-formed
Tag names must be in lowercase
All XHTML elements must be closed

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 in nested lists, is to forget that the inside list must be within an li element, like this:

<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.

Documents Must Be Well-formed

All XHTML elements must be nested within the <html> root element. All other elements can have sub (children) elements. Sub elements must be in pairs and correctly nested within their parent element. The basic document structure is:

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

Tag Names Must Be in Lower Case

This is because XHTML documents are XML applications. XML is case-sensitive. Tags like <br> and <BR> are interpreted as different tags.

This is wrong:

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

This is correct:

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

All XHTML Elements Must Be Closed

Non-empty elements must have an end 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 either have an end tag or the start tag must end with />.

This is wrong:

This is a break<br>
Here comes a horizontal rule:<hr>
Here's an image <img src="happy.gif" alt="Happy face">

This is correct:

This is a break<br />

Here comes a horizontal rule:<hr />

Here's an image <img src="happy.gif" alt="Happy face" />

IMPORTANT Compatibility Note:

To make your XHTML compatible with today's browsers, you should add an extra space before the "/" symbol like this: <br />, and this: <hr />.

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