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.
以下的常數由此延伸定義,只在這個延伸被編譯成PHP或實行時期被動態載入時有效。