title: Regex: non-word-char preceded by space or at the beginning of a line
body: <p>I'm trying to match <code>@</code>'s that are preceeded by nothing or whitespace like in the following example:</p>
  
  <pre><code>@one
      @two 
      who@three
      /@four
  </code></pre>
  
  <p>My approach is <code>(^|\s)@</code>, but this captures <code>one two three four</code>. <code>\s@</code> only captures <code>two</code>. How do I get <code>one two</code>, without getting <code>three four</code>?</p>
  
  <p>If it's relevant, all <code>@</code>'s are succeeded by a letter.</p>