https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Template%21AttributeHelper.php/function/AttributeHelper%3A%3AmergeCollections/11.x
function AttributeHelper::mergeCollections | Drupal API
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https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Template%21AttributeHelper.php/function/AttributeHelper%3A%3AmergeCollections/9
function AttributeHelper::mergeCollections | Drupal API
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