Fundamentals
A domain about the layers that run underneath the frameworks, rather than how to use any one framework or library. It cuts across disciplines, so there is something to read whether you arrive from the frontend or the backend.
For now the Web Engineering Fundamentals Guide is the only one here. It works on two axes: how the machinery works, and how to narrow down a cause from what you can observe. The parts divide it by discipline, and each chapter opens with the chapters it assumes. Read it start to finish, or drop into whichever discipline is giving you trouble.