Control Unity's Script Execution Order by code

ScriptExecutionOrder.cs

using UnityEngine;
using System;
#if UNITY_EDITOR
using UnityEditor;
#endif

public class ScriptExecutionOrder : Attribute
{
    public int order;
    public ScriptExecutionOrder(int order) { this.order = order; }
}

#if UNITY_EDITOR
[InitializeOnLoad]
public class ScriptExecutionOrderManager
{
    static ScriptExecutionOrderManager()
    {
        foreach (MonoScript monoScript in MonoImporter.GetAllRuntimeMonoScripts())
        {
            if (monoScript.GetClass() != null)
            {
                foreach (var attr in Attribute.GetCustomAttributes(monoScript.GetClass(), typeof(ScriptExecutionOrder)))
                {
                    var newOrder = ((ScriptExecutionOrder)attr).order;
                    if (MonoImporter.GetExecutionOrder(monoScript) != newOrder)
                        MonoImporter.SetExecutionOrder(monoScript, newOrder);
                }
            }
        }
    }
}
#endif

/*
// USAGE EXAMPLE
[ScriptExecutionOrder(100)]
public class MyScript : MonoBehaviour
{
        // ...
}
*/

[DefaultExecutionOrder(100)]

https://forum.unity.com/threads/undocumented-but-public-defaultexecutionorder-attribute.530618/

What license is this under?