code: function setTag($tag, $with_ns = false) {
  		$with_ns = $with_ns || (strpos($tag, ':') !== false);
  		if ($with_ns) {
  			$this->tag = $tag;
  			$this->tag_ns = null;
  		} elseif ($this->getTag() !== $tag) {
  			$this->tag_ns[1] = $tag;
  			$this->tag = (($this->tag_ns[0]) ? $this->tag_ns[0].':' : '').$tag;
  		}
  	}
docs: Set tag (with or without namespace)
  @param string $tag
  @param bool $with_ns Does $tag include namespace?
  @see getTag()