title: RegEx for detecting base64 encoded strings
body: <p>I need to detect strings with the form <strong>@base64</strong> (e.g. <code>@VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==</code>) in my application.</p>
  
  <p>The @ has to be at the beginning and the charset for base64 encoded strings is <code>a-z</code>, <code>A-Z</code>, <code>0-9</code>, <code>+</code>, <code>/</code> and <code>=</code>. Would be the appropiate regular expresion to detect them?</p>
  
  <p>Thanks</p>