title: Insert spaces into string using string.format
body: <p>I've been using C# String.Format for formatting numbers before like this (in this example I simply want to insert a space):</p>
  
  <pre><code>String.Format("{0:### ###}", 123456);
  </code></pre>
  
  <p>output:</p>
  
  <pre><code>"123 456"
  </code></pre>
  
  <p>In this particular case, the number is a string. My first thought was to simply parse it to a number, but it makes no sense in the context, and there must be a prettier way.</p>
  
  <p>Following does not work, as ## looks for numbers</p>
  
  <pre><code>String.Format("{0:### ###}", "123456");
  </code></pre>
  
  <p>output:</p>
  
  <pre><code>"123456"
  </code></pre>
  
  <p>What is the string equivalent to # when formatting? The awesomeness of String.Format is still fairly new to me.</p>