title: manually exclude some symbols from [NSCharacterSet letterCharacterSet] invertedSet]
body: <p>The code below will remove all symbols from myString.  Is there a shortest way to make some exclusive symbols (say ')from being removed while still be able to use this code?</p>
  
  <pre><code>myString = [[myString componentsSeparatedByCharactersInSet:[[NSCharacterSet letterCharacterSet] invertedSet]] componentsJoinedByString:@""];
  </code></pre>