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{Tutorial}HTML XHTML.Step 23.


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What Is XHTML?


    XHTML stands for EXtensible HyperText Markup Language

    XHTML is almost identical to HTML 4.01

    XHTML is a stricter and cleaner version of HTML 4.01

    XHTML is HTML defined as an XML application

    XHTML is supported by all major browsers.




Many pages on the internet contain "bad" HTML.


The following HTML code will work fine if you view it in a browser (even if it does NOT follow the HTML rules):

<title>This is bad HTML</title>
<h1>Bad HTML
<p>This is a paragraph


XML is a markup language where documents must be marked up correctly and "well-formed".


The Most Important Differences from HTML


Document Structure

    XHTML DOCTYPE is mandatory
    The XML namespace attribute in <html> is mandatory
    <html>, <head>, <title>, and <body> is mandatory

XHTML Elements

    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 Attributes

    Attribute names must be in lower case
    Attribute values must be quoted
    Attribute minimization is forbidden

<!DOCTYPE ....> Is Mandatory

<!DOCTYPE html PUBLIC "-//MrHF//DTD XHTML 1.0 Transitional//EN"

<html xmlns="http://www.mrhotfire.com/2012/xhtml">

<title>Title of document</title>




XHTML Elements Must Be Properly Nested


<b><i>This text is [b]bold[/b] and [i]italic[/i]</b></i>

XHTML Elements Must Always Be Closed
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

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

This is wrong:

<P>This is a paragraph</P>

This is correct:

<p>This is a paragraph</p>

Attribute Names Must Be In Lower Case

This is wrong:

<table WIDTH="100%">

This is correct:

<table width="100%">

Attribute Minimization Is Forbidden

This is wrong:

<input checked>
<input readonly>
<input disabled>
<option selected>

This is correct:

<input checked="checked">
<input readonly="readonly">
<input disabled="disabled">
<option selected="selected">


How to Convert from HTML to XHTML

    Add an XHTML <!DOCTYPE> to the first line of every page
    Add an xmlns attribute to the html element of every page
    Change all element names to lowercase
    Close all empty elements
    Change all attribute names to lowercase
    Quote all attribute values


Credits Olympus,Internet,ME.

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