Low-Level Design Concepts

Each concept covers what it is, why it exists, how it works, its variants and tradeoffs, and when to use it. Designs link here instead of re-explaining the basics.

Concept	What it covers
UML Basics: Class Diagrams	Every class-diagram notation (class box, visibility, the six relationships, multiplicity, interfaces, enums, generics), what it means, when to use it, the matching Python code and Mermaid syntax