code: function getNamespace() {
  		if ($this->tag_ns === null) {
  			$a = explode(':', $this->tag, 2);
  			if (empty($a[1])) {
  				$this->tag_ns = array('', $a[0]);
  			} else {
  				$this->tag_ns = array($a[0], $a[1]);
  			}
  		}
  
  		return $this->tag_ns[0];
  	}
docs: Get namespace of node
  @return string
  @see setNamespace()