xdiff
PHP 手册

预定义常量

以下常量由本扩展模块定义,因此只有在本扩展模块被编译到 PHP 中,或者在运行时被动态加载后才有效。

XDIFF_PATCH_NORMAL (integer)
This flag indicates that xdiff_string_patch() and xdiff_file_patch() functions should create result by applying patch to original content thus creating newer version of file. This is the default mode of operation.
XDIFF_PATCH_REVERSE (integer)
This flag indicated that xdiff_string_patch() and xdiff_file_patch() functions should create result by reversing patch changed from newer content thus creating original version.

xdiff
PHP 手册