title: Regex -Check if string start with zero + space or zero alone
body: <p>I have this regular expression to math:</p>
  
  <ul>
  <li>String start with a zero + white space + anything else </li>
  <li><p>String is a zero</p>
  
  <pre><code>"0 fkvjdm" // Must Match
  "0" // Must match
  "0.56" // NOT match
  </code></pre></li>
  </ul>
  
  <p>Here is the regular expression I'm using:</p>
  
  <pre><code>^([0]$|([0]\s+.))
  </code></pre>
  
  <p>Is there a way to improve it? or, is it has a bug?</p>
  
  <p>Thanks a lot for your help.</p>
  
  <p>Environment</p>
  
  <ul>
  <li>VS 2010 .net 4</li>
  </ul>