world wide web万维网英文课件：ch02-Introduction to XHTML.ppt

Chapter 2 Introduction to XHTML 2.1 Origins and Evolution of HTML HTML was defined with SGML Original intent of HTML: General layout of documents that could be displayed by a wide variety of computers Recent versions: HTML 4.0 – 1997 Introduced many new features and deprecated many older features HTML 4.01 - 1999 - A cleanup of 4.0 XHTML 1.0 - 2000 Just 4.01 defined using XML, instead of SGML XHTML 1.1 – 2001 Modularized 1.0, and drops frames We’ll stick to 1.1, except for frames 2.1 Origins and Evolution of HTML (continued) Reasons to use XHTML, rather than HTML: HTML has lax syntax rules, leading to sloppy and sometime ambiguous documents– XHTML syntax is much more strict, leading to clean and clear documents in a standard form HTML processors do not even enforce the few syntax rule that do exist in HTML The syntactic correctness of XHTML documents can be validated 2.2 Basic Syntax Elements are defined by tags (markers) Tag format: Opening tag: name Closing tag: /name The opening tag and its closing tag together specify a container for the content they enclose 2.2 Basic Syntax (continued) Not all tags have content If a tag has no content, its form is name / The container and its content together are called an element If a tag has attributes, they appear between its name and the right bracket of the opening tag Comment form: !-- … -- Browsers ignore comments, unrecognizable tags, line breaks, multiple spaces, and tabs Tags are suggestions to the browser, even if they are recognized by the browser 2.3 HTML Document Structure Every XHTML document must begin with: ?xml version = ″1.0″? !DOCTYPE html PUBLIC ″-//w3c//DTD XHTML 1.1//EN″ /TR/xhtml11/DTD/xhtml11.dtd html, head, title, and body are required in every document The whole document must have html as its root html must have the xmlns attribute: html xmlns = ″/1999/xhtml″ A document consists of a head and a body The title tag is used to give the document a title, which is normally displayed in the brows