title: Double forward slash period in regular expression
body: <p>I've recently started using regular expressions in Java and I ran into a strange expression.</p>
  
  <p>The problem asks to find "words" consisting of only letters and at most one concluding period.
  So for example, if I input the string:</p>
  
  <pre><code>one two. wr7ng not1 three. nope..
  </code></pre>
  
  <p>The engine will find one, two and three as the matching words. The given solution for the problem is this Pattern:</p>
  
  <pre><code>for (String tok : s.split(" ")) {
    if (tok.matches("[a-zA-Z]+//.?")) {
      // code done to record successful match
    }
  }
  </code></pre>
  
  <p>What do the two forward slashes mean? I compared this expression with this one:</p>
  
  <pre><code>[a-zA-Z]+.?
  </code></pre>
  
  <p>And found only the latter incorrectly accepted digits in the final slot (the period). Is this the only difference?</p>