Unity3D: GUI control name explanation.

GUIControlEditorWindow.cs

using UnityEngine;
using UnityEditor;
using System.Collections;

public class GUIControlEditorWindow : EditorWindow {
	
	[MenuItem("Window/GUIControl Test")]
	public static void OpenGUIControlEditorWindow() {
		EditorWindow.GetWindow<GUIControlEditorWindow>();
	}
	
	private string username;
	private string password;
	private string fullName;
	private string address;
	private string noFocusName;
	private string focus;
	
	private void OnGUI() {
		EditorGUILayout.BeginVertical("Box");
		GUI.SetNextControlName("Username");
		username = EditorGUILayout.TextField("Username", username);
		
		GUI.SetNextControlName("Password");
		password = EditorGUILayout.TextField("Password", password);
		
		GUI.SetNextControlName("Full name");
		fullName = EditorGUILayout.TextField("Full name", fullName);
		
		EditorGUILayout.LabelField("Address");
		GUI.SetNextControlName("Address");
		address = EditorGUILayout.TextArea(address, GUILayout.Height(50f));

		noFocusName = EditorGUILayout.TextField("No focus name", noFocusName);
		EditorGUILayout.EndVertical();
		
		// Set focus control.
		EditorGUILayout.BeginVertical("Box");
		focus = EditorGUILayout.TextField("Name", focus);
		if (GUILayout.Button("Focus")) {
			GUI.FocusControl(focus);
		}
		EditorGUILayout.EndVertical();

		// Focus control debug.
		EditorGUILayout.BeginVertical("Box");
		EditorGUILayout.LabelField("Focus on: " + GUI.GetNameOfFocusedControl());
		EditorGUILayout.EndVertical();
	}
	
}