XHTML

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XHTML

• http//www.w3schools.com/xhtml/

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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

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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 isnt very good at either

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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 well-formed (syntactically
correct)
All browsers can display HTML
All modern browsers display XML, but in various
ways
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From HTML to XHTML, I

• XHTML elements must be properly nested
• ltbgtltigtbold and italiclt/bgtlt/igt is wrong
• XHTML documents must be well-formed
• lthtmlgtltheadgt ... lt/headgtltbodygt ...
  lt/bodygtlt/htmlgt
• Tag names must be in lowercase
• All XHTML elements must be closed
• If an HTML tag is not a container, close it like
  thisltbr /gt, lthr /gt, ltimg src"smile.gif" /gt
• Note Some older browsers require a space before
  the /

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From HTML to XHTML, II

• Attribute names must also be in lower case
• Example lttable width"100"gt
• Attribute values must be quoted
• Example lttable width"100"gt
• Attribute minimization is forbidden
• Example ltframe noresize"noresize"gt,cannot be
  abbreviated to ltframe noresizegt
• The id attribute replaces the name attribute
• Wrong ltimg src"picture.gif" name"picture1" /gt
• Right ltimg src"picture.gif" id"picture1" /gt
• Best ltimg src"picture.gif" name"picture1"
  id"picture1" /gt

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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

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DOCTYPE declaration, I

• Every XHTML document must begin with one of the
  DOCTYPE declarations (DTDs)
• lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Strict//EN" "http//www.w3.org/TR/xhtml1/DTD/xhtml
  1-strict.dtd"gt
• lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Transitional//EN" "http//www.w3.org/TR/xhtml1/DTD
  /xhtml1-transitional.dtd"gt
• lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Frameset//EN" "http//www.w3.org/TR/xhtml1/DTD/xht
  ml1-frameset.dtd"gt
• lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML
  1.1//EN "http//www.w3.org/TR/xhtml11/DTD/xhtml1
  1.dtd"gt
• (Essentially the same as XHTML 1.0 Strict)

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DOCTYPE declaration, II

• The main DTDs are as follows
• 1.0 Strict
• 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
• 1.0 Transitional
• Use with standard HTML and/or with CSS
• Allows deprecated HTML elements
• 1.0 Frameset
• Use if your document uses HTML frames
• 1.1
• Like 1.0 Strict, but with added support for
  Chinese

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An XHTML Example

• lt!DOCTYPE html PUBLIC"-//W3C//DTD XHTML 1.0
  Strict//EN" "http//www.w3.org/TR/xhtml1/DTD/xhtml
  1-strict.dtd"gtlthtml xmlns"http//www.w3.org/1999
  /xhtml" xmllang"en"
  lang"en"gt ltheadgt lttitlegtA simple
  documentlt/titlegt lt/headgt ltbodygt
  ltpgtA simple paragraph.lt/pgt lt/bodygtlt/htmlgt

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Extension

• A file containing an HTML page should have the
  extension .html
• According to W3C, an XHTML page should have the
  extension .xhtml
• However...
• I have had trouble getting JavaScript to work on
  pages with this extension
• I recommend sticking with .html, at least for now

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Tools

• Dave Raggett's HTML TIDY,http//tidy.sourceforge.
  net/,is a free UNIX tool for checking and
  cleaning up HTML pages
• The W3C HTML Validation Toolhttp//validator.w3.o
  rg/ is an HTML form for checking (but not fixing)
  HTML and XHTML documents

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Vocabulary

• SGML Standard Generalized Markup Language
• HTML Hypertext Markup Language
• XHTML eXtensible Hypertext Markup Language
• XML eXtensible Markup Language
• DTD Document Type Definition

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The End