extension implementation problems

Hello My name is Rui Marques and i work with php for quite some time now. About an year ago my interest turned on xml. To parse that information i chose "domxml_xmltree" simply because i needed a tree of data, exposed in php objects and arrays. Now i have 4 more projects which depend on that function on (4.2.2 version). My question is, how can i copy-paste that function source and create a personal module for future (and past) versions of php (unix based)? I know that the question is very generic, all i need is the place and direction to start my "quest"! Would it be easier if i create a "new_domxml_xmltree" in php? Another question is that, in http://www.php.net/manual/en/function.domxml-xmltree.php is mentioned that the function is experimental, does that mean that this function could sease to exist in future versions, or simple stop being documented? thanks for your time, best regards, Rui Marques