We have a special decoration library that allows for dependency inversion for components. It lives in src/mongo/util.

Notable classes include:

• Decoration
• Decorable
• DecorationContainer
• DecorationRegistry

Decorations are occasionally surprising, it's important that we make it clear how and when these objects are allocated, constructed, destructed, and deallocated.

Since decorations are mostly used in conjunction with context objects, we can document them as a single section in src/mongo/util/README.md.

This is intended to be abstract documentation, describe relationships and state transitions not code in common language.