title: How to allow only a certain number of words?
body: <p>Say I have a Scanner, and a user adds two words to that scanner.</p>
  
  <p>There should be no space before the first word.</p>
  
  <p>Only one space between the two words.</p>
  
  <p>And no space after the second word.</p>
  
  <p>i.e. </p>
  
  <pre><code>'hello world' is correct
  </code></pre>
  
  <p>but</p>
  
  <pre><code>'hello world bye' 
  ' hello world' 
  'hello word ' 
  'hello  world'
  </code></pre>
  
  <p>are all incorrect.</p>
  
  <p>I've tried to use regex, but with no success. </p>
  
  <p>EDIT: Only letters a to z allowed (uppercase and lower)</p>