Attributes in Unity 3D

What is an Attribute:
Attributes provide a powerful method of associating metadata, or declarative information, with code (assemblies, types, methods, properties, and so forth). -Taken from .NET.

The Script:
I have compiled some example code to help you learn how to use C# Attributes in Unity. Below is an example of what I believe are the most useful attributes. Everything is fully commented and is ready to add to a GameObject in your Unity game.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

//[RequireComponent(typeof(OtherClass))]      // This makes is so this component requires another component. (unity will auto add it for you)
[DisallowMultipleComponent]                 // This makes it so you cannot add the same component twice.
[HelpURL("https://docs.unity3d.com/2018.2/Documentation/ScriptReference/AddComponentMenu.html")]// This will link out to a help doc through unity when clicking on the ? book in the inspector
public class LearnAttributesScript : MonoBehaviour
{
    [Header("Stats")]                       // This will be bold.
    public int health;
    public int armor;
    [Header("Character Info")]
    public string playerName;
    [Tooltip("This crates a paragraph like area of text")]  // This creates a mouse over tip. When you mouse over the text 'description' in the editor.
    [TextArea]
    public string description;
    [Space]                                 // This creates a space inbetween this and the lower item. 
    public int level;
    [Tooltip("This keeps something with in two numbers")]
    [Range(1, 100)]                         // This keeps something with in two numbers
    public int powerlvl;
    [HideInInspector]                       // This hides data or a class that needs to be pulbic but only altered through code, not the inspector. 
    public bool isPaused;

    /////////////////////////
    [Tooltip("Right click on this to see menu options")]
    [ContextMenuItem("One", "SelectOne")]   // This creates a menu system.
    [ContextMenuItem("Two", "SelectTwo")]
    [ContextMenuItem("Three", "SelectThree")]
    [Multiline(4)]                          // This creates an indented multiline string.
    public string a_number = "";
    void SelectOne()
    {
        a_number = "You selected 1!";
    }
    void SelectTwo()
    {
        a_number = "You selected 2!";
    }
    void SelectThree()
    {
        a_number = "You selected 3!";
    }
    /////////////////////////
    [ContextMenu("Do Something")]               // Creates selectable code to be accessed in the gear icon.
    void DoSomething()
    {
        Debug.Log("Perform operation");
    }
    /////////////////////////
    [UnityEditor.MenuItem("Tools/Do a thing")]  // Creates a menu with a selectable item that will run code.
    public static void DoAThing()
    {
        Debug.Log("a thing");
    }
}

Other Info on Attributes:

Another helpful Attribute is [Serializable] and [SerializeField]. These are a bit more complicated then a one sentence comment will allow but here and here is some basic info on them.

Here are the Unity Docs on Attributes which are somewhat useful.
Here is a really helpful video.

How do you use Attributes? Thank you for reading,
James