title: How to add several values to the same key
body: <p>how can I add several values to the same key? Something like this:</p>
  
  <pre><code>x = {}
  x["k1"] =  nil
  x["k1"] &lt;&lt; {"a" =&gt; "a"}
  x["k1"] &lt;&lt; {"b" =&gt; "b"}
  </code></pre>
  
  <p>well, this doesn't work like with array. </p>