XHTML

XHTML

• Reference: "W3C Web Internationalization Tutorials" at http://www.w3.org/International/tutorials/
• XHTML is "HTML fixed up"
• HTML loosely followed SGML guidelines
• XML is based on SGML but very much simplified, following experience with HTML
• XML is more SGML-compliant than HTML
• e.g. <br> in HTML should bre represented as either <br/> or <br> </br> in XML
• Most HTML browser will cope with XHTML as long as some guidelines are followed e.g. write <br/> as <br />

XHTML - HTML or XML?

• An XHTML document can be treated as an HTML document
• An XHTML document can be treated as an XML document
• Ooops! Some differences
  • An HTML document should start with a DOCTYPE header

    
    	    <!DOCTYPE doctype PUBLIC "-//w3c//dtd html 4.0 transitional//en">
    	    

  • An XML document should start with

    
    	    <?xml version="1.0" encoding=".."?>
    	    

  • An XHTML document should have both

    
    	    <?xml version="1.0" encoding=".."?>
    	    <!DOCTYPE doctype PUBLIC "-//w3c//dtd html 4.0 transitional//en">
    	    

• Some browsers (e.g IE) don't properly support XML documents and so will misinterpret the second two forms
• Browsers that do support XML properly should use the second two forms

Encoding

• The default HTML encoding is ISO-8859-1 (IETF RFC2854)
• The default XML encoding is UTF-8 or UTF-16
• The HTTP server can set/override the encoding, but not all XML documents are sent by HTTP
• Documents should include an encoding declaration

  
  	    <?xml version="1.0" encoding="utf-8"?>
  	    

  or

  
  	    <?xml version="1.0" encoding="utf-8"?>
  	    <!DOCTYPE doctype PUBLIC "-//w3c//dtd html 4.0 transitional//en">
              ...
              <meta http-equiv="Content-type" content="text/html;charset=UTF-8">
  	    

Charset

• Both XML and HTML use the Unicode character set
• The <#XXXX; notation stands for a Unicode code point
• The <#XXXX; notation does not stand for a code point in the current encoding e.g. in the Windows 1252 encoding, the euro is <#x80;. However, it is <x20AC; in Unicode, and this value must be used
• HTML has aliases such as <accute;. These do not exist in XML unless the DTD explicitly defines them, and XHTML does not
• A document could be written just using Unicode code points, and would be the same under all encodings. To make it more readable, an encoding that can represent all characters directly shold be used e.g. UTF-8 or UTF-16