FeedWriter\Feed::getNamespacePrefixes PHP Method

    private function getNamespacePrefixes()
    {
        $prefixes = array();
        // Get all tag names from channel elements...
        $tags = array_keys($this->channels);
        // ... and now all names from feed items
        foreach ($this->items as $item) {
            foreach (array_keys($item->getElements()) as $key) {
                if (!in_array($key, $tags)) {
                    $tags[] = $key;
                }
            }
        }
        // Look for prefixes in those tag names
        foreach ($tags as $tag) {
            $elements = explode(':', $tag);
            if (count($elements) != 2) {
                continue;
            }
            $prefixes[] = $elements[0];
        }
        return array_unique($prefixes);
    }