Traits/Document/Taggeable.php
public function addTag($item)
    {
        if (!in_array($item, $this->tags)) {
            $this->tags[] = $item;
        }

        return $this;
    }
public function addTag($item)
    {
        if (!in_array($item, $this->tags)) {
            $this->tags[] = $item;
        }

        return $this;
    }
Add tag

@return collection $tags

@return self