how to enable objects?

The following code doesn't seem to do anything in the standard php distribution that I have set up. I encountered some information in the manual that suggests php works with this object-style of coding. But is there something I have to do to enable php to deal with objects? Is there a module or something that I have to install? If so, how do I go about locating and installing it? code example: ================= $chapter_array->rewind(); $iterator=$chapter_array->getIterator(); echo $iterator->current(); echo $iterator->key(); Thanks in adfvance for any information.