【Tags and Layers】
1、tags and layers 配置面板。"Edit" -> "Project Settings" -> "Tags and Layers"来打开设置面板。
2、tag可以理解为一类元素的标记，如hero、enemy、apple-tree等。通过设置tag，可以方便地通过GameObject.FindWithTag()来寻找对象。
GameObject.FindWithTag()只返回一个对象，要想获取多个tag为某值的对象，GameObject.FindGameObjectsWithTag()。
可以在Inspector中设置tag。一个对象只能有一个tag。
3、sorting layer
Unity uses the concept of sorting layers to allow you to divide sprites into groups for overlay priority. Sprites with a sorting layer lower in the order will be overlaid by those in a higher sorting layer. Sometimes, two or more objects in the same sorting layer can overlap (eg, two player characters in a side scrolling game). The order in layer property can be used to apply consistent priorities to sprites in the same layer. As with sorting layers, the rule is that lower numbers are rendered first and can be obscured by the higher numbers rendered later.
4、Layers
Layers are most commonly used by Cameras to render only a part of the scene, and by Lights to illuminate only parts of the scene. But they can also used by raycasting to selectively ignore colliders or to create collisions.
在inspector中可以设置layer
在Camera的Culling Mask中可以设置渲染哪些Layers。
意即，在使用过程中，使用Culling Mask、Layer Mask的地方实际指的就是layer。
