PHP, ProcessWire function: Get fields inside fieldsets of Template or Page objects. Choose to retrieve FieldsArray or values as WireData.

getFieldsetOf.php

/**
 * getFieldsetOf
 *
 * for ProcessWire
 * 
 * gets fields inside a fieldset of pages or templates
 * choose to retrieve values
 * 
 * @param  Template|Page         $context                   the page or template
 * @param  String                $fieldsetName              name of the fieldset
 * @param  bool|boolean          $collectValues             want to collect values of the pages fieldset?
 * @param  string                $fieldsetCloseIdentifier   default: '_END'
 * @return FieldsArray|WireData                             returns FieldsArray or if data wanted, WireData
 */
function getFieldsetOf($context, String $fieldsetName, $collectValues = false, $fieldsetCloseIdentifier = '_END') {    

    if ($collectValues === true && $context instanceof Page) {
        $collectedItems = new WireData();
    } else if($context instanceof Template) {
        $collectValues = false;
        $collectedItems = new FieldsArray();
    } else {
        throw new WireException("getFieldsetOf: first argument must be of type Page or Template", 1);
    }

    if (!$context->fieldgroup->get($fieldsetName . $fieldsetCloseIdentifier)) return NULL;

    $collecting = false;
    foreach ($context->fieldgroup as $field) {
        if ($field->name == $fieldsetName) {
            $collecting = true;
            continue;
        }
        if ($field->name == $fieldsetName . $fieldsetCloseIdentifier) {
            break;
        }
        if ($collecting) {
            if ($collectValues) {
                $collectedItems->set($field->name, $context->get($field->name));
            } else {
                $collectedItems->add($field);
            }
        }
    }
    return $collectedItems;
}