title: replaceCharactersInRange Not Working As Expected?
body: <p>I have an NSMutableString that holds the string "I have ∞ Hours and ∞ Min to spare." and I am trying to replace the first ∞ with a "0" by doing</p>
  
  <pre><code>NSMutableString *timeString = [NSMutableString stringWithString:@"And I have ∞ Hours and ∞ Min to spare."];
  NSLog(@"%@",timeString);
  [timeString replaceCharactersInRange:NSMakeRange(11,12) withString:@"0"];
  NSLog(@"%@",timeString);
  </code></pre>
  
  <p>However, instead of only replacing the first ∞, it replaces the phrase "∞ Hours and "</p>
  
  <p>Here is what is printed out in console:</p>
  
  <pre><code>And I have ∞ Hours and ∞ Min to spare.
  And I have 0∞ Min to spare.
  </code></pre>
  
  <p>I don't understand why its deleting characters beyond the specified range.</p>