The first stop on this tour is also one of the more important ones: options related to the language interpreter. The first item here is the engine variable, which controls whether the PHP engine should be "on" or "off". Turning the engine off means that embedded PHP code will not be parsed by the Web server. It doesn't usually make sense to do this, so leave it on.
engine = On

The short_open_tag variable controls whether the parser should recognize the shortcut <?...?> tags, as well as the standard <?php...?> tags. Turn this off if you anticipate conflicts with other languages, or if you want to apply strict syntactical rules to your PHP code.
short_open_tag = On

Normally, session, cookie or HTTP header data in a PHP script must be sent before any output is generated by the script. If this is not possible in your application, you can enable what PHP calls output buffering, with the output_buffering variable.

With output buffering on, PHP stores the output of your script in a special memory buffer and sends it only when explicitly told to do so. This allows you to send special HTTP headers and cookie data even in the middle or at the end of your script; however, it can degrade performance marginally.
output_buffering = Off

You can also pass the output_buffering variable a number indicating the size of the buffer, for example:
output_buffering = 2048

When PHP starts up, it adds a message stating its version number to the Web server's standard header. To turn this off, set the expose_php variable to false. This is useful if, for example, you want to mask the capabilities of your Web server from potential hackers.
expose_php = On