xpath examples & domxpath use with drupal

When the wonderful Feeds module can not be used it is useful to know how to use domxpath and to write queries.
usage:

$dom = new DOMDocument();
@$dom->loadHTML($html);
$xpath = new DOMXPath($dom);

to get the text inside of a particular tag

$result = $xpath->query("//div[@id='my_id']");
$text = $result->item(0)->nodeValue
// or easier $xpath->query("//div[@id='my_id']/text()");

to get id's of items with a specific class

$results = $xpath->query("//div[contains(@class,'my_class')]");
foreach($results as $result) {
  $id= $result->getAttribute('id');
}

to extract whole DOM html

$result= $this->xpath("//body");
$body = $dom->saveHTML($result->item(0));
//or easier $result= $this->xpath("//body/node()");

FOR UNIT TESTING
to test if link inside of a specific tag exists

$this->xpath("//div[@id='my_id']//a[contains(@href, 'my_link')]");

to test a div containing a string

// exact text
$this->xpath("//div[contains(@class, 'views-field-field-vintage')]/div[.='2010']");
// containing text
$this->xpath("//div[contains(@class, 'views-field-field-vintage')]/span[contains(., '2010')]");

to test the nth item

//this checks that inside the 3rd image field is an image of 70 width with style my_style_preset
$this->xpath("(//td[contains(@class, 'views-field-field-singleimage')])[3]/img[@width=70 and contains(@src, '/styles/my_style_preset/')]");
// do not forget the parenthesis

some complex stuff

"//td[contains(@class, 'xl7717818') or contains(@class, 'xl6717818') or contains(@class, 'xl7817818') or contains(@class, 'xl7917818')][text()!='A']/../following-sibling::tr[contains(@height, 20)]"
// td OR condition and td does not have "A" text then 1 level up in the dom (to the tr tag) then select the next tr that has an height attribute of 20

traversing + position

preceding-sibling::tr[1]/td[position()>2 and position()<5]
// move to the previous tr then get all the td in position 3 and 4

tag that contains some text

//td[contains(., 'Division')]

Display errors - WSOD

The bootstrap override the values you could set to display error ad the reporting level. To be 100% sure everything is printed out when something fails in a blank screen (wsod), make index.php like this:

Properly render a field

Drupal offers a few (sometimes complicated...) solutions to output a field. Lets take an example with a date field.
To display the full rendered field: field_view_field()