php.ini directives introduced in PHP 5.2.0:
This useful option makes it possible to differentiate between standard file operations on remote files, and the inclusion of remote files. While the former is usually desirable, the latter can be a security risk if used naively. Starting with PHP 5.2.0, you can allow remote file operations while disallowing the inclusion of remote files in local scripts. In fact, this is the default configuration.
PCRE's backtracking limit.
PCRE's recursion limit. Please note that if you set this value to a high number you may consume all the available process stack and eventually crash PHP (due to reaching the stack size limit imposed by the Operating System).
New directives in PHP 5.2.2: