Every Web browser interprets HTML and CSS tags a little differently. Tables, forms, and graphic positioning and alignment tags will all work a bit differently in each brand or operating system version of Web browser. These subtleties normally pass unnoticed, but in very precise or complex Web page layouts they can lead to nasty surprises. Never trust the implementation of HTML, CSS, JavaScript, Java, or any plug-in architecture until you have seen your Web pages displayed and working reliably in each brand of browser. If significant numbers of your readers are using the Macintosh, Linux, or UNIX operating systems, you should also test your more complex pages and programming functionality in those operating systems. Unfortunately, platform-specific bugs remain common in the major Web browsers.