XHTML http www w3schools com xhtml Jan 14 2019 What is XHTML XHTML stands for Extensible Hypertext Markup Language XHTML is aimed to replace HTML XHTML is almost identical to HTML 4 01 XHTML is a stricter and cleaner version of HTML XML Extensible Markup Language is a markup language designed for describing data XHTML is HTML redefined as an XML application XHTML is a bridge between HTML and XML 2 The problem with HTML HTML started out as a way of way of describing the structure of documents with tags to indicate headers paragraphs and the like Because people wanted to control the appearance of documents HTML acquired tags to control fonts alignment etc The result is a markup language that does both but isn t very good at either 3 HTML vs XML XML looks a lot like HTML but HTML uses a fixed set of tags With XML you make up your own tags and define what they mean in a separate document HTML is designed to display data to humans XML is designed to describe data to computers Browsers are very tolerant of errors in HTML XML documents must be wellformed syntactically correct All browsers can display HTML All modern browsers display XML but in various ways 4 From HTML to XHTML I XHTML elements must be properly nested b i bold and italic b i is wrong XHTML documents must be well formed html head head body body html Tag names must be in lowercase All XHTML elements must be closed If an HTML tag is not a container close it like this br hr img src smile gif Note Some older browsers require a space before the 5 From HTML to XHTML II Attribute names must also be in lower case Attribute values must be quoted Example table width 100 Attribute minimization is forbidden Example table width 100 Example frame noresize noresize cannot be abbreviated to frame noresize The id attribute replaces the name attribute Wrong img src picture gif name picture1 Right img src picture gif id picture1 Best img src picture gif name picture1 id picture1 6 SGML and DTDs SGML stands for Standard Generalized Markup Language HTML XHTML XML and many other markup languages are defined in SGML A DTD or Document Type Definition describes the syntax to use for the current document There are three different DTDs for XHTML you can pick the one you want These DTDs are public and on the web You must start your XHTML document with a reference to one of these DTDs 7 DOCTYPE declaration I Every XHTML document must begin with one of the DOCTYPE declarations DTDs DOCTYPE html PUBLIC W3C DTD XHTML 1 0 Strict EN http www w3 org TR xhtml1 DTD xhtml1 strict dtd DOCTYPE html PUBLIC W3C DTD XHTML 1 0 Transitional EN http www w3 org TR xhtml1 DTD xhtml1transitional dtd DOCTYPE html PUBLIC W3C DTD XHTML 1 0 Frameset EN http www w3 org TR xhtml1 DTD xhtml1 frameset dtd 8 DOCTYPE declaration II The three main DTDs are as follows Strict Transitional Use for really clean markup with no display information no font color or size information Use with CSS Cascading Style Sheets if you want to define how the document should look Use with standard HTML and or with CSS Allows deprecated HTML elements Frameset Use if your document uses HTML frames 9 An XHTML Example DOCTYPE html PUBLIC W3C DTD XHTML 1 0 Strict EN http www w3 org TR xhtml1 DTD xhtml1 strict dtd html head title A simple document title head body p A simple paragraph p body html 10 Tools Dave Raggett s HTML TIDY http www w3 org People Raggett tidy is a free UNIX tool for checking and cleaning up HTML pages W3C HTML Validation Tool http validator w3 org is an HTML form for checking but not fixing HTML and XHTML documents 11 Vocabulary SGML Standard Generalized Markup Language HTML Hypertext Markup Language XHTML eXtensible Hypertext Markup Language XML eXtensible Markup Language DTD Document Type Definition 12 The End 13
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