Webmaster''''s Guide to the Wireless Internet part 13 pot

92 Chapter 3 • A New Markup: WML Response.AddHeader "Cache-Control", "no-cache, must-revalidate" Response.AddHeader "Pragma", "no-cache" %> NOTE In addition to checking how the individual device handles caching, be aware that WAP gateways may employ caching technology as well, which can be harder to identify. Bookmarking Bookmarking works much in the same way as Web browsing, allowing a user to mark a page of interest so that they can return directly to the page at a later date. Sometimes you may not want a user to bookmark your page (such as when the URL also contains information specific to that particular session).You can control bookmarking on the Openwave platform with the following meta information: <meta name="vnd.up.markable" forua="true" content="false"/> Understanding the Deck of Cards Paradigm A WML file uses a “deck of cards” paradigm to structure content.Think of each file as a deck, within which are any number of cards. Each card is a single page that can be displayed on the device.A simple WML file containing two cards within the deck would look like the following: <?xml version="1.0"?> <!DOCTYPE wml PUBLIC "//WAPFORUM//DTD_WML_1.1//EN" http://www.wapforum.org/DTD/wml_1.1.xml> <! Start of the deck > <wml> <! Card 1 > <card> </card> <! Card 2 > www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 92 A New Markup: WML • Chapter 3 93 <card> </card> <! End of the deck > </wml> Decks are extremely handy for sending the user groups of pages that they are likely to access, meaning that the user has to make only one connection to download several separate cards. WML Elements The previous example introduced the concepts of decks and cards.You may have noticed that the structure of the deck looked a lot like HTML. In fact,WML is quite similar to HTML in its use of elements and attributes to describe the con- tent within each file.The <wml> and <card> elements in the example are just two examples of the elements you’ll find in the WML language. Adding Attributes Most WML elements have at least one attribute that you can use to define parameters that specify how the device should handle the element.The element’s attribute(s) are placed in the opening element and an attributes’ values are enclosed in either single quotes (') or double quotes ("). Here is an example of how an element containing two attributes would appear: <element attribute1="value1" attribute2="value2">text</element> WARNING As you can see in the example in this section, there is a space between each attribute. This is required in the WML specification; failure to sepa- rate each element with a space will cause the WML to fail to load. You will see that most of the elements in the WML Elements section of this book contain several different attributes that you can set to specify how the element will be used. www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 93 94 Chapter 3 • A New Markup: WML The id and class Attributes The id and class attributes respectively allow specific elements or groups of ele- ments to be individually identified and manipulated.An id may be assigned only once within a particular deck and is thus unique in that instance, whereas a class may be assigned to many different elements within the deck and is thus useful for grouping similar elements.You can have multiple class names within the class attribute, but these should be separated by white space.A class is case-sensitive, so class1 and Class2 are two separate entities. NOTE For each WML element detailed in the sections following this one, a table shows the various attributes that each element can contain. Because id and class are core attributes that can be applied to any WML element, for the sake of repetition, they will not be shown within each individual element attribute table. The <a> Element The <a> element is an abbreviated form of the <anchor> element.Text within the <a> element forms a hyperlink to another card or deck. It is preferable to use <a> instead of <anchor> wherever possible.You cannot nest the <a> ele- ment, and it may only contain either a <br> or <img> element.The following is an example of the syntax for the <a> element: <a href="deck2.wml">A Link to Deck 2</a> The href attribute is required.All other attributes are optional. See Table 3.2 for a list of attributes for the <a> element. Table 3.2 Attributes for the <a> Element Attribute Name Description href The target location for the link title A short string of text that identifies the element xml:lang The natural or formal language of the element www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 94 A New Markup: WML • Chapter 3 95 The <access> Element The <access> element allows the author to control how the deck is accessed from other areas.You should consider the use of an <access> element when the privacy and security of the information being accessed is important.The use of variables within WML (a situation that does not exist within HTML) could theo- retically allow malicious manipulation of information. By restricting access at the deck level, the user’s information can be kept private. The <access> element works by specifying which particular domains and/or paths are allowed to access the deck.When the deck is accessed, the user agent checks to see whether the requested destination is allowed access from the cur- rent deck. If the domain and/or path do not match those specified, access is not allowed. Domains are evaluated according to suffix order.Thus, www.thedomain.com is a match for thedomain.com, but domain.com will not match. Similarly, paths are matched according to prefix.Thus, /path/path/ will match path/path but /pathpath will not. The default for the domain attribute is the domain where the current deck is located, and the path attribute defaults to “/”.A deck may contain only one <access> element. See Table 3.3 for a list of attributes for the <access> element. Table 3.3 Attributes for the <access> Element Attribute Name Description domain The particular domain that may access the deck path The particular path that may access the deck The following is an example of the syntax for the <access> element: <access domain="domain.com" path="/path"/> In this example, the referring Uniform Resource Identifier (URI) would be allowed access to the deck: http://domain.com/path/deck.wml. The <anchor> Element The behavior of the <anchor> element is specified by the task it contains.A task can be thought of as an action that must be performed as a result of the user selecting the element. In the case of the <anchor> element, this can be either <go>, <prev>, or <refresh>, but must consist of one task only. <Anchor> ele- ments cannot be nested. See Table 3.4 for a list of attributes for the <anchor> element. www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 95 96 Chapter 3 • A New Markup: WML Table 3.4 Attributes for the <anchor> Element Attribute Name Description accesskey Signifies the access key that is assigned to the element title A short string of text that identifies the element The following is an example of the syntax for the <anchor> element: <anchor> A link to Deck 2 <go href="deck2.wml"> </anchor> As you can see, this example uses a <go> task to perform the same task as the example given for the <a> element. NOTE For both the <a> and <anchor> elements, the URI can be relative or absolute. Additionally, URL fragments are identified in the same way as anchors in HTML by using the # identifier. The <b> Element The <b> element signifies that the text contained within should be rendered by the user-agent as a bold font. Note that many WML microbrowsers do not render text marked up as bold with a bold font, so if you are relying on con- veying meaning with bold, check with the target device for conformity. It is perhaps a better idea (and is suggested within the WML specification) that text should use <strong> or <em> elements instead, resorting to using <b> only where specific control of the text is required.This will be familiar to anyone who has studied the use of <bold> versus <strong> within HTML.Table 3.5 lists the attribute for the <b> element. Table 3.5 Attribute for the <b> Element Attribute Name Description xml:lang The natural or formal language of the element www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 96 A New Markup: WML • Chapter 3 97 The following is an example of the syntax for the <b> element: This text is normal text, but <b>this text is bold text!</b> The <big> Element The <big> element indicates that the user-agent should render the text in a larger font size than the base font size for the device.Table 3.6 lists the attribute for the <big> element. Table 3.6 Attribute for the <big> Element Attribute Name Description xml:lang The natural or formal language of the element The following is an example of the syntax for the <big> element: This text is a normal size <big>but this text is bigger!</big> The <br/> Element The <br/> element forces a line break wherever it is placed within the text. Table 3.7 lists the attribute for the <br/> element. Table 3.7 Attribute for the <br/> Element Attribute Name Description xml:lang The natural or formal language of the element The following is an example of the syntax for the <br/> element: This is on one line.<br/>This is on the next line. The <card> Element Each WML deck can contain one or more cards.The <card> element acts as a container for text and other elements that together form discrete units for display in a device.The id of a card can be used as the target for a fragment identifier within any navigation element. See Table 3.8 for a list of attributes for the <card> element. www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 97 98 Chapter 3 • A New Markup: WML Table 3.8 Attributes for the <card> Element Attribute Name Description newcontext This can be true or false and specifies if the user-agent should reinitialize upon entry. The default value is false. onenterbackward This is an event that is fired upon entry to the card as a result of a <prev> task. onenterforward This is an event that is fired upon entry to the card as a result of <go> task. ontimer This is an event that fires when a timer expires. ordered This can be true or false and specifies whether the content of the card should be displayed in an ordered fashion. The default value is true. title Specifies the title of the card. This is typically displayed by the user-agent to provide meaning to the user for the purpose of the card and should be kept short and descriptive. xml:lang The natural or formal language of the element. The following is an example of the syntax for the <card> element: <card title="A New Card" newcontext="true"> This is a card. </card> All attributes of the card element are implied—that is, they are not absolutely necessary: <card> This is a card. </card> This code is just as valid as the prior example. However, you should at least include a title in all of your cards if only to give users some sort of indication what the card is about. The <do> Element In certain situations, you may want to interact with the user in some way.The <do> element provides an interface to initiate actions from your users at the deck or card level. If the <do> element is present at the deck level, it can be www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 98 A New Markup: WML • Chapter 3 99 contained within a template element to provide the same functionality to all cards within the deck.A <do> within a card will override a <do> within the parent deck if they share the same name. Exactly how the interface is rendered to the user is entirely dependent of the device, and the <do> may take the appearance of a soft button, a link, or choice through the menu system.You can use the type attribute to provide some indica- tion to the user-agent as to the intended use of the <do> element. See Table 3.9 for a list of attributes for the <do> element. Table 3.9 Attributes for the <do> Element Attribute Name Description label A text label that identifies the element. name The name of the event binding. optional This can be either true or false. If true, this element may be ignored by the user-agent. type The intended function for which the element is intended. xml:lang The natural or formal language of the element. NOTE The type attribute is required and must be specified at all times. Note that the <do> element may not be rendered where it is placed within the text of the card. In fact, the only safe assumption you can make is that the user-agent will map the element to a specific user interface. This can cause problems because the <do> element can appear at the top of the rendered card, at the bottom, in the middle—in fact just about any- where—so you must carefully consider the use of the <do> element with respect to the target device. The following is an example of the syntax for the <do> element: <do type="accept" label="Next Card"> <go href="#nextcard"/> </do> www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 99 100 Chapter 3 • A New Markup: WML The <em> Element The <em> element specifies that the text should be rendered by the user-agent with emphasis.Table 3.10 lists the attribute for the <em> element. Table 3.10 Attribute for the <em> Element Attribute Name Description xml:lang The natural or formal language of the element The following is an example of the syntax for the <em> element: This text is normal but <em>this text is emphasized</em>. The <fieldset> Element The <fieldset> element is useful for grouping similar fields and text together to allow better representation of the contents on the target device.You can nest further <fieldset> elements to provide more information on how the fields and text relate to each other. See Table 3.11 for a list of attributes for the <fieldset> element. Table 3.11 Attributes for the <fieldset> Element Attribute Name Description title The title of the fieldset, which is typically used to describe the contents of the fieldset, and may also be rendered by the user-agent to provide information on the content to the user. xml:lang The natural or formal language of the element. The following is an example of the syntax for the <fieldset> element: <fieldset title="Ice-Creams"> Strawberry<br/> Vanilla<br/> Chocolate </fieldset> www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 100 A New Markup: WML • Chapter 3 101 The <go> Element The <go> element is a task that specifies navigation to a URI.The href attribute is required. See Table 3.12 for a list of attributes for the <go> element. Table 3.12 Attributes for the <go> Element Attribute Name Description accept-charset Used to specify the character set the server should accept. The default is to use the character set the deck was sent in. cache-control If cache-control is set to no-cache, the URL must be reloaded from the server. This allows new values to be set and sent to the server in the case of submissions sending data pairs. enctype Used when the method is set to post, enctype specifies the content type that the submission should be sent as. The default value is application/x-www- form-urlencoded. href The destination that should be navigated to. method Either post or get. The go method is exactly the same as the submission method used in HTTP. sendreferer This is either true or false, and if true, the user-agent must send the URI of the deck that contains the<go> element to the server. This allows access controls to be exercised. The following is an example of the syntax for the <go> element: <go href="card1.wml"/> You can find further examples of navigating using the <go> element later in this chapter in the section called “Creating WML Content.” The <head> Element The <head> element contains data relating to the deck as a whole.The following is an example of the syntax for the <head> element: <head> <access domain="domain.com"/> </head> www.syngress.com 159_wg_wi_03 10/22/01 4:33 PM Page 101 . at the top of the rendered card, at the bottom, in the middle—in fact just about any- where—so you must carefully consider the use of the <do> element with respect to the target device. The. ordered fashion. The default value is true. title Specifies the title of the card. This is typically displayed by the user-agent to provide meaning to the user for the purpose of the card and should. rendered to the user is entirely dependent of the device, and the <do> may take the appearance of a soft button, a link, or choice through the menu system.You can use the type attribute to provide