public function setCharacters(Array $characters)
	{
		if (count($characters) !== count(array_filter($characters, 'is_string'))) {
			throw new \InvalidArgumentException(
				__METHOD__."() expects parameter one, characters, to be an array of "
					. "strings"
			);	
		}
		
		$this->characters = $characters;
		
		return $this;
	}