title: jQuery - show/hide DIVs is they have a certain class
body: <p>Here is my code :</p>
  
  <pre><code>  &lt;div id="principal" class="classxx"&gt;
      &lt;div class="class001 cat2 blabla"&gt;
        &lt;div class="class002"&gt;
          &lt;div class="class003"&gt;&lt;/div&gt;
          &lt;div class="class004"&gt;&lt;/div&gt;
          &lt;div class="class005"&gt;&lt;/div&gt;
        &lt;/div&gt;
      &lt;/div&gt;
      &lt;div class="class001 cat3 blabla"&gt;
        &lt;div class="class002"&gt;
          &lt;div class="class003"&gt;&lt;/div&gt;
          &lt;div class="class004"&gt;&lt;/div&gt;
          &lt;div class="class005"&gt;&lt;/div&gt;
        &lt;/div&gt;
      &lt;/div&gt;
      &lt;div class="class001 cat1 blabla"&gt;
        &lt;div class="class002"&gt;
          &lt;div class="class003"&gt;&lt;/div&gt;
          &lt;div class="class004"&gt;&lt;/div&gt;
          &lt;div class="class005"&gt;&lt;/div&gt;
        &lt;/div&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  </code></pre>
  
  <p>I need a function like :</p>
  
  <pre><code>function showOnlyCat(className){}
  </code></pre>
  
  <p>If I call <code>showOnlyCat('cat3')</code> I want to see only all the DIVs that have the 'cat3' class (each DIV having multiple classes) and its children of course
  The function has to target only first children of DIV#principal</p>
  
  <p>And I also need a <code>showAllCat()</code> that shows all the children DIVs of DIV#principal</p>
  
  <p>Thank you VERY MUCH for your help</p>