title: How to use rangeOfString in Swift?
body: <p>Firstly, I'm trying to figure out the function of “rangeOfString”. In my own understanding, I think "rangeOfString" is the function to find some specify thing in the string, like a word. Such as the word "a" is the first part of "apple". How this explanation show in the function's return. And the NSRange is return type of that function. Due to my poor English, I can not the understand the Official Reference for 'NSRange'.  </p>
  
  <p>Questions are:</p>
  
  <ol>
  <li>Is my understanding of "rangeOfString" correct?</li>
  <li>How to use this function? How to set parameters in that function?           </li>
  </ol>
  
  <p>A big appreciate for your guidance and helping.</p>
  
  <p>Ethan Joe</p>