title: TextBox Custom Attribute is Empty
body: <p>I am setting a custom attribute in the markup like this..</p>
  
  <pre><code>&lt;asp:TextBox runat="server" guid="" ID="txtlocation1" type="text" class="autocomplete short-field require" name="location1" autocomplete="off" datasource="locations" /&gt;
  </code></pre>
  
  <p>Javascript sets the value of it and I am trying to read the value on button click like this...</p>
  
  <pre><code>var val = txtlocation1.Attributes["guid"];
  </code></pre>
  
  <p>I always get an empty string.. any ideas? 
  PS: I am not setting the attribute in code though.</p>