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.
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.