$pl = new PageList();
$pl->filterByAttribute('category_listing_categories','Doors','='); 
$pages = $pl->get();
foreach( $pages AS $page){
   echo '<p>'.$page->getCollectionName().', '. $page->getAttribute('category_listing_categories').'</p>';
         }

$pl->filterByAttribute('category_listing_categories','%Doors%', 'like');

$pl->filterByAttribute('category_listing_categories','%Doors%', 'like');

$pl->filter(false, "(ak_category_listing_categories LIKE '%\nDoors\n%')");

//DEV NOTES:
// * PageList filter() takes an attributeValue's name, not its ID
// * Attributes of type "select" wrap values in newline characters when saved to the database -- seehttp://www.concrete5.org/developers/bugs/5-4-1-1/select-type-attrib...
// * We can't use magic method filterByRelatedContentCategory() because that only searches on equality
//   (which isn't appropriate with a multi-select option like this -- there could be more than 1 value saved).
// * PageList filter() method has an undocumented feature where you pass in false for the 1st arg 
//   and a SQL "WHERE" clause (well, a portion of one) for the 2nd arg -- seehttp://www.concrete5.org/developers/pro-accounts/community-leaders-...

foo($ak,$av){
  $pl = new PageList();
   $pl->filterByAttribute($ak, '%'.$av.'%', 'like'); 
   $pages = $pl->get();
  return $pages;
}

$pl->filterByAttribute($ak, "%\n{$av}\n%", "like");

foo($ak,$av){
  $pl = new PageList();
   $pl->filterByAttribute($ak1, '%'.$av1.'%', 'like'); 
   $pl->filterByAttribute($ak2, '%'.$av2.'%', 'like'); 
   $pages = $pl->get();
  return $pages;
}

$ak1 = CollectionAttributeKey::getByHandle('your_attribute_handle');
if (!is_null($ak1)) {
  //do the filter for your_attribute_handle here
}
$ak2 = CollectionAttributeKey::getByHandle('your_other_attribute_handle');
if (!is_null($ak2)) {
  //do the filter for your_other_attribute_handle here
}

Loader::model('attribute/type');
Loader::model('attribute/categories/collection');
$ak = CollectionAttributeKey::getByHandle('your_attribute_handle_goes_here');
$satc = new SelectAttributeTypeController(AttributeType::getByHandle('select'));
$satc->setAttributeKey($ak);
$options = $satc->getOptions();

$aks = CollectionAttributeKey::getAllKeys();
echo '<select>';
foreach( $aks AS $key ){
  echo "<option value=\"{$key->handle}\">{$key->name}</option>";
}
echo '</select>';

$link = $nh->getLinkToCollection($page);

if (!is_null($page->getCollectionPointerExternalLink())) {
    $link = $page->getCollectionPointerExternalLink();
} else {
    $link = $nh->getLinkToCollection($page);
}