Unity3D Editor Tooltip

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public GUIContent(string text, string tooltip);

using UnityEngine;
using System.Collections;
public class ExampleClass : MonoBehaviour {
void OnGUI() {
GUI.Button(new Rect(0, 0, 100, 20), new GUIContent("Click me", "This is the tooltip"));
GUI.Label(new Rect(0, 40, 100, 40), GUI.tooltip);
}
}

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[Tooltip("My tooltip")]
public string remoteUrl;