title: Regular Expression: match only non-repeated occurrence of a character
body: <p>I need to find and replace all occurrences of apostrophe character in a string, but only if this apostrophe is not followed by another apostrophe.</p>
  
  <p>That is </p>
  
  <blockquote>
    <p>abc'def</p>
  </blockquote>
  
  <p>is a match but </p>
  
  <blockquote>
    <p>abc''def</p>
  </blockquote>
  
  <p>is NOT a match.</p>
  
  <p>I've already composed a working pattern -  <code>(^|[^'])'($|[^'])</code> but I believe it may be shorter and simpler.</p>
  
  <p>Thanks,</p>
  
  <p>Valery</p>