php|architect's Guide to Web Scraping with PHP - Wind Business ...

DOM Extension ” 101
// Buffer DOM errors rather than emitting them as warnings
$oldSetting = libxml_use_internal_errors(true);
// Instantiate a container for the document
$doc = new DOMDocument;
// Load markup already contained within a string
$doc->loadHTML($htmlString);
// Load markup saved to an external file
$doc->loadHTMLFile($htmlFilePath);
// Get all errors if needed
$errors = libxml_get_errors();
// Get only the last error
$error = libxml_get_last_error();
// Clear any existing errors from previous operations
libxml_clear_errors();
// Revert error buffering to its previous setting
libxml_use_internal_errors($oldSetting);
?>
T r T e r m i n o l o g y
Once a document is loaded, the next natural step is to extract desired data from it.
H o w e v e r, doing so requires a bit more knowledge about how the DOM is structured.
Recall the earlier mention of tree parsers. If you have any computer science background,
you will be glad to know that the term “ t r e e ” in the context of tree parsers
does in fact refer to the data structure by the same name. If not, here is a brief rundown
of related concepts.
A tree is a hierarchical structure (think family tree) composed of nodes, which exist
in the DOM extension as the DOMNode class. N o d e s are to trees what elements are to
arrays: just items that exist within the data structure.
Each individual node can have zero or more child nodes that are collectively represented
by a childNodes property in the DOMNode class. childNodes is an instance
of the class DOMNodeList, which is exactly what it sounds like. Other related proper-