The controlID of the control that has keyboard focus.

	// Click on the text field to see the id of the control.
	
	private var str : String = "A String!";
	function OnGUI() {
		str = GUILayout.TextField(str,10);
		Debug.Log("id: " + GUIUtility.keyboardControl);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    private string str = "A String!";
    void OnGUI() {
        str = GUILayout.TextField(str, 10);
        Debug.Log("id: " + GUIUtility.keyboardControl);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	private str as string = 'A String!'

	def OnGUI() as void:
		str = GUILayout.TextField(str, 10)
		Debug.Log(('id: ' + GUIUtility.keyboardControl))