code: 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
docs: 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