t_types_by_ext</span>[<span class="ruby-identifier">ext</span>] <span class="ruby-operator">&lt;&lt;</span> <span class="ruby-identifier">klass</span><span class="ruby-operator">::</span><span class="ruby-constant">CONTENT_TYPE</span>
    }
  }

  <span class="ruby-keyword">self</span>.<span class="ruby-identifier">defaults</span> = [ <span class="ruby-constant">RubyXL</span><span class="ruby-operator">::</span><span class="ruby-constant">ContentTypeDefault</span>.<span class="ruby-identifier">new</span>(<s