WAP and WML are in their infancies, at about the same maturity level that HTML and the Web were four to five years ago. Developers learned the hard way from HTML, with its wildly inconsistent browser support, that standards are crucial. As a result, WML was implemented from the get-go as an XML (Extensible Markup Language) application, ensuring that all WML documents are well formed. XML applications don't allow the lax coding common with HTML documents, thus minimizing display variations among today's browsers. A big reason why browsers render many Web pages inconsistently is that, when the browser meets an improper HTML document, the browser's behavior is undefined. Different browser vendors elected different treatments; the result is widely varying presentations of the same document. To eliminate this problem, the W3C (World Wide Web Consortium) expressed HTML 4.0 in XML to produce XHTML. WML, on the other hand, started as an XML application.

In addition to being an XML application, WML has some subtle differences from HTML that make it better suited for small devices with limited bandwidth. For example, a WML page is known as a card; related cards form decks. A deck of cards shares one common set of headers and is downloaded in its entirety when one member card is requested. This saves on bandwidth because headers are not sent for each card. This setup also makes the Web site more responsive as the user navigates between different cards in the same deck.

WML also has variables, which are part of the WML definitions and don't need any extra scripting support. HTML does not support variables, and thus relatively complex client- or server-side scripts are required to track simple information. For example, if you require users to log on to your site, you will need to use hidden form elements, cookies, query strings or server-side scripts to track the user's identity. In WML, you can simply declare a "userid" variable and assign it the value of the logged in user's identity. Since a golden rule in WML is not to send any requests to the server unless absolutely necessary, and because cell phones typically have tiny and weak processors, this addition is very advantageous. In fact, this is one feature that I could have made extensive use of in HTML.

Another element that can be accomplished with scripting, but that makes complete sense as a native construct, is a timer. WML has the concept of a timer as a native tag; when the timer expires, an event such as navigation to the subsequent card in the deck can be invoked.

Before we dig too deeply into the specifics of WML, let's examine how a WML page is served from a server to the micro browser. Any leading Web server can be used to serve WML documents; you just need to configure it with some new MIME types. This task varies by Web server, but it is a routine system administration function and should not be difficult. Following are the MIME entries that need to be configured by the server:

• text/vnd.wap.wml for .wml files (WML source files)

• application/vnd.wap.wmlc for .wmlc files (WML compiled files)

• text/vnd.wap.wmlscript for .wmls files (WMLScript source files)

• application/vnd.wap.wmlscriptc for .wmlsc files (WMLScript compiled files)

• image/vnd.wap.wbmp for .wbmp files (wireless bitmaps)

The other function of the gateway is to translate secure communications. The Internet's standard for secure communication is SSL (Secure Socket Layer). The wireless world does not use SSL, however; it uses instead a protocol known as WTLS (Wireless Transport Layer Security). Thus, the WAP gateway talks WTLS to the phone and SSL to the Web server, performing the intermediate translation. WAPDrive Ltd., one of the best WAP sources on the Internet, has compiled a list of WAP gateways. The list, which can be found at www.wapdrive.com/DOCS/wap_gateway/index.html, includes some free gateways and others for which you have to register and pay. Typically, your service provider will run its own gateway, which you can access through your wireless phone. If you are a developer and would like to run your own gateway, visit www.kannel.org, which provides an open-source WAP gateway.