Customizing the Unity Editor - Mastering Unity Scripting - page 259

Renamed objects using the Batch Rename tool
C# attributes and reflection
From this point forward in the chapter, all editor extensions will rely heavily on
the concepts of attributes and reflection. These concepts are not specific to Unity
but refer to more general ideas in computer science, programming, and to their
application in languages such as C# as well as in the .NET framework. Before
proceeding to the next editor extension, let's consider attributes and the related
concept of reflection using the example of the Range attribute, which is native to
Unity. Consider the following line of code:
public float MyNumber = 0;