Core PHP Programming, Third Edition

1.6. What a PHP Script Looks Like

PHP exists as a tag inside an HTML file. Like all HTML tags, it begins with a less than symbol, or opening angle bracket (<), and ends with a greater than symbol, or closing angle bracket (>). To distinguish it from other tags, the PHP tag has a question mark (?) following the opening angle bracket and preceding the closing angle bracket. All text outside the PHP tag is simply passed through to the browser. Text inside the tag is expected to be PHP code and is parsed.

To accommodate XML and some picky editors such as Microsoft's Front Page, PHP offers three other ways to mark code. Putting php after the opening question mark makes PHP code friendly to XML parsers. Alternatively, you may use a script tag as if ...