RadTextBox renders several <input> elements. The control's client ID is applied to the next <input> in the HTML, which is also seen on your screenshot.
someID - this is the ID of the <input> which holds the control's actual value and the client control instance
someID_text - this is the ID of the <input> which accepts the user input
Rendering several <input> elements is required in order to support all features of RadTextBox (and the other RadInput textbox types)
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