History Leading to XHTML SGML (Standard Generalized Markup Language) can be used with almost any type of document stored in almost any format introduced in the 1980s metalanguage– used to created other languages HTML confusing standards among browsers derived from SGML XML (Extensible Markup Language) also used to design markup languages a “lite” version SGML
History Leading to XHTML - continued XHTML is a reformulation of HTML, written in XML Versions of XHTML In 2009, the W3C discontinued definition of XHTML 2.0 in favor of HTML 5
Well Formed and Valid Documents An XML document (including XHTML) with correct syntax is a well-formed document. A well-formed document with correct content and structure is a valid document. A Document Type Definition (DTD) specifies correct content and structure.
3 DTDs Are Associated with XHTML 1.0 Transitional supports many of the presentational features of HTML, including the deprecated elements and attributes. Best used for older documents that contain deprecated features. Frameset used for documents containing frames, and also supports deprecated elements and attributes. Strict does not allow any presentational features or deprecated HTML elements and attributes. Does not support frames or inline frames. It is best used for documents that need to strictly conform to the latest standards.
Rules for Well-Formed XHTML
Rules for Well-Formed XHTML XHTML documents must have a single root element that contains all other elements. This root element is, of course, <html> Attribute minimization, when some attributes lack an attribute value, is not allowed in XHTML.
Prohibited Elements in Valid XHTML applet: alternative for inserting Java applets basefont: set font properties center: centered text dir: another list type font: set font properties iframe: inline frames isindex: alternative to <input> tag for text menu: another list type s: strikethrough text strike: strikethrough text u: underlined text
Prohibited Children in Valid HTML <body> <body> <img src=“pic.gif” /> <p><img src=“pic.gif” /></p> </body> </body>
Prohibited Attributes in Valid XHTML
Required Attributes in Valid XHTML
Initial Declarations in XHTML Documents: Step 1 The first line of an XHTML document should contain a declaration indicating that the document adheres to the rules and syntax of XML Enter the following as the first line of the file: <?xml version=“value” encoding=“type” standalone=“type” ?> Where the version attribute indicates the XML version of the document, the encoding attribute specifies the character encoding, and the standalone attribute indicates whether the document contains references to an external DTD.
Initial Declarations in XHTML Documents: Step 2 Add a DOCTYPE declaration to indicate which DTD you’re using:
Initial Declarations in XHTML Documents: Step 3 A namespace is a unique identifier for elements and attributes originating from a particular document type (like XHTML or MathML) The default namespace is applied to a root element and any element within it. It is declared with:
Testing an XHTML Document To test your document, you need to send the file to an XML parser or an XHTML validator. The W3C provides an XHTML validator on their website: http://validator.w3.org You upload your file to the site and get a report:
Report Showing a Successful Validation
Validating XHTML with Style Sheets Validators can get confused by some stylesheets: <style type=“text/css”> p > img {float: left} < /style> You must separate the file into PCDATA and CDATA. Parsed character data (PCDATA) is text to be parsed by a browser or parser. Unparsed character data (CDATA) is text not to be processed by the browser or parser. A CDATA section marks a block of text as CDATA so that parsers ignore any text within it: <! [CDATA[ ]]>
Tips for Converting old HTML Code to XHTML 1. Include an xml declaration in the first line of your file so that your document can be accessed by XML parsers. 2. Add a DOCTYPE declaration for one of the XHTML DTDs and check your document for well-formedness and validity whenever you make a change to the code. 3. Add the XHTML default namespace to the html element of your document. 4. Make sure that all element and attribute names are in lowercase letters and that all attribute values are placed in quotes. 5. Make sure that all empty elements are entered as one-sided tags. Look especially for improper syntax in the img, hr, and br elements. 6. Make sure that all two-sided tags are properly closed. Old HTML code often does not have closing tags for the p element.
Tips for Converting old HTML Code to XHTML 7. Make sure that all inline images contain the alt attribute. 8. Look for deprecated attributes such as align, bgcolor, and background and replace them with the float (or text-align), background-color, and background-image styles. 9. Replace the name attribute with the id attribute 10. Fix all instances of attribute minimization. 11. Replace the use of the font element with either the span element or with a style that applies the same formatting specified by the font element. 12. Replace the use of the width attribute in the td or th element with the width style.