FriBiDi is a free implementation of the Unicode Bidirectional Algorithm.
You must download and install the FriBiDi package.
To enable FriBiDi support in PHP you must compile --with-fribidi[=DIR] where DIR is the FriBiDi install directory.
由于这些常量是由该扩展模块定义的,因此只有在该扩展模块被编译到 PHP 中,或者在运行时被动态加载后,这些常量才有效。