title: Regular expression to allow alphanumeric, only one space and then alpahnumeric
body: <p>I've searched and searched and tried many different ways, but I can't seem to figure this out. I'm looking for a way to only allow alphanumeric characters, then only one space, then alphanumeric characters. I'm sure it's easy, but I don't know it.</p>
  
  <p>Examples of what I want:</p>
  
  <pre>
      First Last     Allowed
      First La-st    Not Allowed
      FirstLast      Not Allowed
      First  Last    Not Allowed
      First La'st    Not allowed
  </pre>
  
  <p>I'd then like to remove the invalid characters from the string.</p>
  
  <p>Please let me know if you need more information. Thanks a lot!</p>