Make a multi-line text field where the user can edit a string.

	var stringToEdit : String = "Hello World\nI've got 2 lines...";
	function OnGUI () {
		// Make a multiline text area that modifies stringToEdit.
		stringToEdit = GUILayout.TextArea (stringToEdit, 200);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    public string stringToEdit = "Hello World\nI've got 2 lines...";
    void OnGUI() {
        stringToEdit = GUILayout.TextArea(stringToEdit, 200);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	public stringToEdit as string = 'Hello World\nI\'ve got 2 lines...'

	def OnGUI() as void:
		stringToEdit = GUILayout.TextArea(stringToEdit, 200)