C# class definition unknown
<p>I am looking through some C# code and I am seeing something I cannot figure out near the class definition.  Here is a sample of what I am seeing.</p>

<pre><code>[MethodImpl(MethodImplOptions.Synchronized)]
public void AddTag(RTag tag)
{
    this.tags.Add(tag)
}
</code></pre>

<p>What the heck is the first line doing or stating?  I have not been able to track it down in any of my reference books.</p>

<p>Thanks!</p>
