Appendix K Introduction to XHTML: Part 1 1437 1 2 4 5 6 7 8 9 10 11 12 13 14 15

Level 1 Header

16

Level 2 header

17

Level 3 header

18

Level 4 header

19

Level 5 header

20

Level 6 header

21 22 23 Fig. K.4 Fig. K.Fig.Fi K.4g. K.44Header elements h1through h6. Fig. K. Header element h1(line 15) is considered the most significant header and is rendered in a larger font than the other five headers (lines 16 20). Each successive header element (i.e., h2, h3, etc.) is rendered in a smaller font. Look-and-Feel Observation K.1 Placing a header at the top of every XHTML page helps viewers understand the purpose of each page.
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1436 Introduction to XHTML: Part 1 Appendix K Testing and Debugging Tip K.1 Use a validation service, such as the W3C HTML Validation Service, to confirm that an XHT- ML document is syntactically correct. K.5 Headers Some text in an XHTML document may be more important than some other. For example, the text in this section is considered more important than a footnote. XHTML provides six headers, called header elements, for specifying the relative importance of information. Figure K.4 demonstrates these elements (h1 through h6). Portability Tip K.1 The text size used to display each header element can vary significantly between browsers. Fig. K.3 XHTML validation results. (Courtesy of World Wide Web Consortium (W3C).)
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Appendix K Introduction to XHTML: Part 1 1435 K.4 W3C XHTML Validation Service Programming Web-based applications can be complex, and XHTML documents must be written correctly to ensure that browsers process them properly. To promote correctly written documents, the World Wide Web Consortium (W3C) provides a validation service (validator.w3.org) for checking a document s syntax. Documents can be validated either from a URL that specifies the location of the file or by uploading a file to the site validator.w3.org/file-upload.html. Uploading a file copies the file from the user s computer to another computer on the Internet. Figure K.2 shows main.html (Fig. K.1) being uploaded for validation. Although the W3C s Web page indicates that the service name is HTML Validation Service,1 the validation service is able to validate the syntax of XHTML documents. All the XHTML examples in this book have been validated successfully through validator.w3.org. By clicking Browse , users can select files on their own computers for upload. After selecting a file, clicking the Validate this document button uploads and validates the file. Figure 4.3 shows the results of validating main.html. This document does not contain any syntax errors. If a document does contain syntax errors, the Validation Service displays error messages describing the errors. In Exercise K.11, we ask readers to create an invalid XHTML document (i.e., one that contains syntax errors) and to check the document s syntax, using the Validation Service. This enables readers to see the types of error messages generated by the validator. Fig. K.2 Validating an XHTML document. (Courtesy of World Wide Web Consortium (W3C).) 1. HTML (HyperText Markup Language) is the predecessor of XHTML designed for marking up Web content. HTML is a deprecated technology.
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1434 Introduction to XHTML: Part 1 Appendix K An XHTML document divides the htmlelement into two sections head and body. Lines 9 11 define the Web page s head section with a head element. Line 10 specifies a title element. This is called a nested element, because it is enclosed in the head element s start and end tags. The headelement also is a nested element, because it is enclosed in the html element s start and end tags. The title element describes the Web page. Titles usually appear in the title bar at the top of the browser window and also as the text identifying a page when users add the page to their list of Favorites or Bookmarks, which enable users to return to their favorite sites. Search engines (i.e., sites that allow users to search the Web) also use the titlefor cataloging purposes. Good Programming Practice K.3 Indenting nested elements emphasizes a document s structure and promotes readability. Common Programming Error K.3 XHTML does not permit tags to overlap a nested element s end tag must appear in the document before the enclosing element s end tag. For example, the nested XHTML tags cause a syntax error, because the enclosing head element s ending tag appears before the nested title element s ending tag. Good Programming Practice K.4 Use a consistent title naming convention for all pages on a site. For example, if a site is named Bailey s Web Site, then the title of the main page might be Bailey s Web Site Links . This practice can help users better understand the Web site s structure. Line 13 opens the document s body element. The body section of an XHTML document specifies the document s content, which may include text and tags. Some tags, such as the paragraph tags (

and

) in line 14, mark up text for display in a browser. All text placed between the

and

tags form one paragraph. When the browser renders a paragraph, a blank line usually precedes and follows paragraph text. This document ends with two closing tags (lines 15 16). These tags close the body and html elements, respectively. The ending tag in an XHTML document informs the browser that the XHTML markup is complete. To view this example in Internet Explorer, perform the following steps: 1. Copy the Appendix K examples onto your machine from the CD that accompanies this book (or download the examples from www.deitel.com). 2. Launch Internet Explorer, and select Open… from the File Menu. This displays the Open dialog. 3. Click the Open dialog s Browse… button to display the Microsoft Internet Explorer file dialog. 4. Navigate to the directory containing the Appendix K examples and select the file main.html; then, click Open. 5. Click OK to have Internet Explorer render the document. Other examples are opened in a similar manner. At this point your browser window should appear similar to the sample screen capture shown in Fig. K.1. (Note that we resized the browser window to save space in the book.)
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Appendix K Introduction to XHTML: Part 1 1433 8 9 10 11 12 13 14

Welcome to XHTML!

15 16 Fig. K.1 Fig. K.Fig.Fi K.1g. K.11First XHTML example. (Part 2 of 2.) Fig. K. XHTML markup contains text that represents the content of a document and elements that specify a document s structure. Some important elements of an XHTML document include the html element, the head element and the body element. The html element encloses the head section (represented by the head element) and the body section (represented by the body element). The head section contains information about the XHTML document, such as the title of the document. The head section also can contain special document formatting instructions called style sheets and client-side programs called scripts for creating dynamic Web pages. The body section contains the page s content that the browser displays when the user visits the Web page. XHTML documents delimit an element with start and end tags. A start tag consists of the element name in angle brackets (e.g., ). An end tag consists of the element name preceded by a / in angle brackets (e.g., ). In this example, lines 8 and 16 define the start and end of the htmlelement. Note that the end tag on line 16 has the same name as the start tag, but is preceded by a /inside the angle brackets. Many start tags define attributes that provide additional information about an element. Browsers can use this additional information to determine how to process the element. Each attribute has a name and a value separated by an equal sign (=). Line 8 specifies a required attribute (xmlns) and value (http://www.w3.org/1999/xhtml) for the html element in an XHTML document. For now, simply copy and paste the htmlelement start tag on line 8 into your XHTML documents. We discuss the details of the html element s xmlns attribute in Chapter 18, Extensible Markup Language (XML). Common Programming Error K.1 Not enclosing attribute values in either single or double quotes is a syntax error. Common Programming Error K.2 Using uppercase letters in an XHTML element or attribute name is a syntax error.
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1432 Introduction to XHTML: Part 1 Appendix K Good Programming Practice K.1 Assign documents file names that describe their functionality. This practice can help you identify documents faster. It also helps people who want to link to a page, by giving them an easy-to-remember name. For example, if you are writing an XHTML document that contains product information, you might want to call it products.html. Machines running specialized software called a Web server store XHTML documents. Clients (e.g., Web browsers) request specific resources, such as the XHTML documents from the Web server. For example, typing www.deitel.com/books/downloads.htminto a Web browser s address field requests downloads.htmfrom the Web server running at www.deitel.com. This document is located in a directory named books. K.3 First XHTML Example In this appendix and the next, we present XHTML markup and provide screen captures that show how Internet Explorer renders (i.e., displays) the XHTML. Every XHTML document we show has line numbers for the reader s convenience. These line numbers are not part of the XHTML documents. Our first example (Fig. K.1) is an XHTML document named main.html that displays the message Welcome to XHTML!in the browser. The key line in the program is line 14, which tells the browser to display Welcome to XHTML!Now let us consider each line of the program. Lines 1 3 are required in XHTML documents to conform with proper XHTML syntax. For now, copy and paste these lines into each XHTML document you create. The meaning of these lines is discussed in detail in Chapter 18, Extensible Markup Language (XML). Lines 5 6 are XHTML comments. XHTML document creators insert comments to improve markup readability and describe the content of a document. Comments also help other people read and understand an XHTML document s markup and content. Comments do not cause the browser to perform any action when the user loads the XHTML document into the Web browser to view the document. XHTML comments always start with . Each of our XHTML examples includes comments that specify the figure number and file name and provide a brief description of the example s purpose. Subsequent examples include comments in the markup, especially to highlight new features. Good Programming Practice K.2 Place comments throughout your markup. Comments help other programmers understand the markup, assist in debugging and list useful information that you do not want the browser to render. Comments also help you understand your own markup when you revisit a document for modifications or updates in the future. 1 2 4 5 6 7 Fig. K.1 Fig. K.Fig.Fi K.1g. K.11First XHTML example. (Part 1 of 2.) Fig. K.
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Appendix K Introduction to XHTML: Part 1 1431 Outline K.1 Introduction K.2 Editing XHTML K.3 First XHTML Example K.4 W3C XHTML Validation Service K.5 Headers K.6 Linking K.7 Images K.8 Special Characters and More Line Breaks K.9 Unordered Lists K.10 Nested and Ordered Lists K.11 Internet and World Wide Web Resources Summary Terminology Self-Review Exercises Answers to Self-Review Exercises Exercises K.1 Introduction In this appendix, we introduce XHTML1 the Extensible HyperText Markup Language. In the next appendix, Introduction to XHTML: Part 2, we introduce more sophisticated XHT- ML techniques, such as tables, which are particularly useful for structuring information from databases (i.e., software that stores structured sets of data). In this appendix, we do not present any C# programming. Unlike procedural programming languages such as C, Fortran, Cobol and Visual Basic, XHTML is a markup language that specifies the format of text that is displayed in a Web browser such as Microsoft s Internet Explorer or Netscape s Communicator. One key issue when using XHTML2 is the separation of the presentation of a document (i.e., the document s appearance when rendered by a browser) from the structure of the document s information. Throughout this appendix and the next, we will discuss this issue in depth. K.2 Editing XHTML In this appendix, we write XHTML in its source-code form. We create XHTML documents by typing them in with a text editor (e.g., Notepad, Wordpad, vi or emacs), saving the documents with either an.html or .htm file-name extension. 1. XHTML has replaced the HyperText Markup Language (HTML) as the primary means of describing Web content. XHTML provides more robust, richer and more extensible features than HTML. For more on XHTML/HTML, visit www.w3.org/markup. 2. As this book was being submitted to the publisher, XHTML 1.1 became a World Wide Web Consortium (W3C) Recommendation. The XHTML examples presented in this book are based upon the XHTML 1.0 Recommendation, because Internet Explorer 5.5 does not support the full set of XHTML 1.1 features. In the future, Internet Explorer and other browsers will support XHTML 1.1. When this occurs, we will update our Web site (www.deitel.com) with XHTML 1.1 examples and information.
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K Introduction to XHTML: Part 1 Objectives To understand important components of XHTML documents. To use XHTML to create World Wide Web pages. To be able to add images to Web pages. To understand how to create and use hyperlinks to navigate Web pages. To be able to mark up lists of information. To read between the lines was easier than to follow the text. Aristophanes
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