Querypath - HTML DOM parsing and manipulation PHP library
Original is abandoned. Fork alive here: https://github.com/GravityPDF/querypath

This is a guide that explains how to parse html,xml documents using querypath. Written from the point of view of web-scraping

Article on ibm.com: Archive.org link
That link is now dead and un-googleable. So its content now can be freely stolen without guilt.

API docs relevant to parsing: http://querypath.org/classes/QueryPath.DOMQuery.html

Quick example

//Create a new QueryPath object and supply it with source $html page
$qp = QueryPath::withHTML($html);
// find desired html nodes
$linkNodes = $qp->find('a')
//Loop through all the links in the page
foreach ($linkNodes as $li) { 
    echo $li->text() ;
}
// Quickly get title text
$titleText = $qp->find('title')->text();

Generally this is the flow:

• We create a querypath object and supply it with the html source.
• Then Various traversing functions can be used to find matching html nodes.
• We can then optionally loop through the nodes
• Finally we can use attr() or text() or other functions to extract from individual nodes

Observe: the traversing functions can accept css/xpath selectors to narrow down the search.

text() // Get combined text contents of each element in the set of matched elements, including their descendants.
attr('src') // Get value of an attribute with a given name.
html() // Get HTML contents of matching node
innerHtml() // Get the HTML contents INSIDE the node.

IMPORTANT: If traversing functions match multiple nodes. The above functions will return data from first node.

Example: find('a') matches multiple links. text() will return text from first link.

htmlqp($html, 'body', array('convert_to_encoding' => 'utf-8'))->children('p.a');

$tr = $this->qp->top('body')->find('table[id="main"]')->find('tr:nth-child(3)');

Here top('body') gets the top most ancestor matching the selector. The next find commands use css selectors.
Same can be written using an xpath

$tr = $this->qp->xpath('//body/table[@id="main"]/tr[3]');

TODO : add more examples as we find them