The classes that are responsible for drawing and handling the user-interaction logic of elements inside Power Inspector are called “Drawers”.
You can think of them as Power Inspector’s unified and more powerful alternative to Unity’s custom editors and property drawers.
The Drawers in Power Inspector are nestable in nature, and most drawers, outside the ones for simple built-in types, actually have multiple member drawers that handle most of the grunt work for them.
For example, the drawer for a GameObject can contain multiple member drawers to handle its components, all of which can contain multiple member drawers for handling their class members.
Note: In Power Inspector 1.0.3 and earlier drawers were referred to as GUI instructions.