The Serializable attribute lets you embed a class with sub properties in the inspector.
You can use this to display variables in the inspector similar to how a Vector3 shows up in the inspector. The name and a triangle to expand its properties. To do this you need create a class that derives from System.Object and give it the Serializable attribute. In JavaScript the Serializable attribute is implicit and not necessary.
class Test extends System.Object { var p = 5; var c = Color.white; } var test = Test ();
using UnityEngine;
[System.Serializable] class Test : System.Object { public int p = 5; public Color c = Color.white; }