title: Different ways of adding to Dictionary
body: <p>What is the difference in <code>Dictionary.add(key, value)</code> and <code>Dictionary[key] = value</code>?</p>
  
  <p>I've noticed that the last version does not throw an <code>ArgumentException</code> when inserting a duplicate key, but is there any reason to prefer the first version?</p>
  
  <p><strong>Edit</strong>: Does anyone have an authoritative source of information about this? I've tried MSDN, but it is as always a wild goose chase :(</p>