title: Regex that matches a string only with question marks
body: <p>How could I write a regex that will match a string containing only question marks</p>
  
  <p>"???"  > true</p>
  
  <p>"????" > true</p>
  
  <p>"? "    > true</p>
  
  <p>"?a?"  > false</p>
  
  <p>"?a"   > false</p>
  
  <p>Thanks in advance !</p>
  
  <p>Edit:
  2 cases I missed:</p>
  
  <p>"? " > true</p>
  
  <p>"??  ? ?" > true</p>