title: WPF: ColumnSpan in UniformGrid
body: <p>I know that <em>UniformGrid</em> haven't attached properties <em>ColumnSpan</em> and <em>RowSpan</em>. But what i really need is container with fixed width and inner cells also with fixed widths, except few UIElements, that should be filled in few cells. 
  For example:</p>
  
  <pre><code>&lt;UniformGrid Columns="4"&gt;   &lt;TextBlock&gt;1&lt;/TextBlock&gt;
  &lt;TextBlock&gt;2&lt;/TextBlock&gt;
  &lt;TextBlock Grid.ColumnSpan="2"&gt;34&lt;/TextBlock&gt;
  </code></pre>
  
  <p>UniformGrid is ideal for me except this situation: last <em>TextBlock</em> is not fill two cells.
  Is it possible use some other solution to give the needed result? 
  Thank you for any advise!</p>
  
  <p>P.S.And... why XAML parser is not stops with error where process this markup? </p>