This image shows the Control Element Structure of the Telerik RadTextBox as displayed by Visual Style Builder:
RadTextBoxElement is created for the purpose of reusability e.g. RadTextBoxElement can be used in RadGridView control. Note: RadTextBoxElement is not a control but element. Refer to Telerik Presentation Framework section about the difference.
FillPrimitive and BorderPrimitive set the overall background and border properties of the control.
The most important node is RadTextBoxItem node which hosts standard .net text box control. There are several implications because of that. The first is that this node cannot be themed. And the second is that events hierarchyis broken at that place e.g. mouse click in the text box field does not propagate to the root element (RadTextBox control).
You can use the following code snippet to access RadTextBoxItem and subscribe to the click event:
[C#] Subscribing for the click event of the RadTextBoxItem
this.radTextBox1.TextBoxElement.TextBoxItem.Click += new EventHandler(TextBoxItem_Click);
[VB.NET] Subscribing for the click event of the RadTextBoxItem
AddHandler RadTextBox1.TextBoxElement.TextBoxItem.Click, AddressOf TextBoxItem_Click