def <<(input)
      if input.index(/\s+/).nil?
        word      = normalize_word input
        self.word = word unless word == ''
      elsif input.scan(SENTENCE_DELIMITER).length < 2
        self.sentence = input.gsub(SENTENCE_DELIMITER, '')
      else
        self.passage = input
      end
    end
def <<(input)
      if input.index(/\s+/).nil?
        word      = normalize_word input
        self.word = word unless word == ''
      elsif input.scan(SENTENCE_DELIMITER).length < 2
        self.sentence = input.gsub(SENTENCE_DELIMITER, '')
      else
        self.passage = input
      end
    end
Prepares selectors and weights storage
 Analyze input and add appropriate part

 Determines if input is word, sentence or passage and adds it

 @param [String] input