When you use XML methods in a script, $this doesn't get set or is buggy. That means you can't use instance variables or methods of that object.

When you run the following script you only get SE,SE,EE,EE but the variables content and instancevar aren't set. The only solution I could think of is that $this points to a wrong object, not the object that the XML methods are called in.

Example script:
<?
class ContentParser
{
    var $parser, $content = "";
    var $instancevar;


    function ContentParser()
    {
        $this->parser = xml_parser_create();
        xml_set_object($this->parser, &$this);
        xml_set_element_handler($this->parser, "start_element", "end_element");
        xml_set_character_data_handler($this->parser, "character_data");
        xml_set_processing_instruction_handler($this->parser, "processing_instruction");
    }

    function parse_text ($data)
    {
        return xml_parse ($this->parser, $data, true);
    }


    function add_content($text)
    {
        $this->content .= $text;
    }

    function processing_instruction($parser, $target, $data)
    {

    }

    function start_element($parser, $name, $attribs)
    {
        echo "SE<br>";
        $this->add_content("Start_element $name<br>");
        $this->instancevar = "I should be set!!!";
    }

    function end_element($parser, $name)
    {
        echo "EE<br>";
        $this->add_content("End element $name<br>");
    }

    function character_data($parser, $data)
    {
        $this->add_content($data);
    }
}

$c = new ContentParser();
$c->parse_text("<document><paragraph>Well this doesn't work. Bug!</paragraph></document>");

echo $c->content; // Zip. No bonus.
echo $c->instancevar;
?>

Am I doing something wrong or is this really a bug?