xdiff
PHP Manual

预定义常量

下列常量由此扩展定义,且仅在此扩展编译入 PHP 或在运行时动态载入时可用。

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 Manual