Appendix L Introduction to XHTML: Part 2 1469 we introduce two new inputtypes. The first type is the radio button (lines 90 113), specified with type “radio”. Radio buttons are similar to checkboxes, except that only one radio button in a group of radio buttons may be selected at any time. All radio buttons in a group have the same nameattribute; they are distinguished by their different valueattributes. The attribute value pair checked = “checked” (line 92) indicates which radio button, if any, is selected initially. The checkedattribute also applies to checkboxes. 1 2 4 5 6 7 8 9 10 11 12 13 14 15

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1468 Introduction to XHTML: Part 2 Appendix L Fig. L.4 Fig. L.Fig..Fi L4g. L.4L.4Form with textareas, password boxes and checkboxes. (Part 3 of 3.) Fig. Common Programming Error L.3 When your form has several checkboxes with the same name, you must make sure that they have different values, or the scripts running on the Web server will not be able to distinguish between them. We continue our discussion of forms by presenting a third example that introduces several more form elements from which users can make selections (Fig. L.5). In this example,
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Appendix L Introduction to XHTML: Part 2 1467 42 Enter your comments here. 44 45

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90 91 92 Fig. L.4 Fig. L.Fig..Fi L4g. L.4L.4Form with textareas, password boxes and checkboxes. (Part 2 of 3.) Fig.
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1466 Introduction to XHTML: Part 2 Appendix L The “password” input in lines 52 53 inserts a password box with the specified size. A password box allows users to enter sensitive information, such as credit card numbers and passwords, by masking the information input with asterisks. The actual value input is sent to the Web server, not the asterisks that mask the input. Lines 60 78 introduce the checkbox formelement. Checkboxes enable users to select from a set of options. When a user selects a checkbox, a check mark appears in the check box. Otherwise, the checkbox remains empty. Each “checkbox” input creates a new checkbox. Checkboxes can be used individually or in groups. Checkboxes that belong to a group are assigned the same name(in this case, “thingsliked”). 1 2 4 5 6 7 8 9 10 11 12 13 14 15

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60 61 62 Fig. L.3 Fig. L.Fig..Fi L3g. L.3L.3Simple form with hidden fields and a textbox. (Part 2 of 2.) Fig. Using method = “post” appends form data to the browser request, which contains the protocol (i.e., HTTP) and the requested resource s URL. Scripts located on the Web server s computer (or on a computer accessible through the network) can access the form data sent as part of the request. For example, a script may take the form information and update an electronic mailing list. The other possible value, method = “get”, appends the
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Appendix L Introduction to XHTML: Part 2 1463 contains the name and path of the desired resource and the method of communication (called a protocol). XHTML documents use the HyperText Transfer Protocol (HTTP). Figure L.3 sends the form data to the Web server, which passes the form data to a CGI (Common Gateway Interface) script (i.e., a program) written in Perl, C or some other language. The script processes the data received from the Web server and typically returns information to the Web server. The Web server then sends the information in the form of an XHTML document to the Web browser. [Note: This example demonstrates client-side functionality. If the form is submitted (by clicking Submit Your Entries), an error occurs.] Forms can contain visual and non-visual components. Visual components include clickable buttons and other graphical user interface components with which users interact. Non-visual components, called hidden inputs, store any data that the document author specifies, such as e-mail addresses and XHTML document file names that act as links. The form begins on line 23 with the form element. Attribute method specifies how the form s data is sent to the Web server. 1 2 4 5 6 7 8 9 10 11 12 13 14 15

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1462 Introduction to XHTML: Part 2 Appendix L Fig. L.2 Fig. L.Fig..Fi L2g. L.2L.2Complex XHTML table. (Part 3 of 3.) Fig. Common Programming Error L.1 When using colspan and rowspan to adjust the size of table data cells, keep in mind that the modified cells will occupy more than one column or row; other rows or columns of the table must compensate for the extra rows or columns spanned by individual cells. If you do not, the formatting of your table will be distorted, and you could inadvertently create more columns and rows than you originally intended. Line 42 introduces attribute valign, which aligns data vertically and may be assigned one of four values “top”aligns data with the top of the cell, “middle”vertically centers data (the default for all data and header cells), “bottom”aligns data with the bottom of the cell and “baseline”ignores the fonts used for the row data and sets the bottom of all text in the row on a common baseline (i.e., the horizontal line to which each character in a word is aligned). L.4 Basic XHTML Forms When browsing Web sites, users often need to provide information such as e-mail addresses, search keywords and zip codes. XHTML provides a mechanism, called a form, for collecting such user information. Data that users enter on a Web page normally is sent to a Web server that provides access to a site s resources (e.g., XHTML documents or images). These resources are located either on the same machine as the Web server or on a machine that the Web server can access through the network. When a browser requests a Web page or file that is located on a server, the server processes the request and returns the requested resource. A request
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76 77 78 Fig. L.2 Fig. L.Fig..Fi L2g. L.2L.2Complex XHTML table. (Part 2 of 3.) Fig.
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