Version 0.6 of PHP client library now released · Friday September 19, 2008 by Crosbie Fitch
The 0.5 version of the PHP API client library has now been completely superseded by a 0.6 incarnation embodied within a MediaWiki extension, that enables demonstrations of the API to occur as part of its documentation.
See contingencymarket.com/Client_APIs for download details.
For example the web page that documents the GetEvent() function also displays the result of a call to it when the page is displayed. See contingencymarket.com/GetEvent.