As far as I can tell this extension requires version 5.2.0 or higher.
It doesn't seem to be stated here anywhere but if you try to use pear to install it then you'll get a message saying that. This has caused me a bunch of grief as I'm not in a position to upgrade on some systems but already have this coded in on other systems.
This extension aims to help parse BBCode text in order to convert it to HTML or another markup language. It uses one pass parsing and provides great speed improvement over the common approach based on regular expressions. Further more, it helps provide valid HTML by reordering open / close tags and by automatically closing unclosed tags.
Since 0.10.1 It supports argument quoting with single quotes, double quotes and HTML escaped double quotes.