title: Why the first letter gets matched in regex
body: <p><strong>UPDATE: actually if I want to match "-" I have to use - when there is something after -</strong></p>
  
  <p>All:</p>
  
  <p>Why in this example:</p>
  
  <pre><code>var a = "Pencil_sharper.pdf"
  a.split(/[. -_]+/g)
  (4) ["", "encil", "sharper", "pdf"]
  </code></pre>
  
  <p>I expected </p>
  
  <pre><code>["Pencil", "sharper", "pdf"]
  </code></pre>