Quickshell is a toolkit you can use to create status bars, widgets, lockscreens and everything else desktop related. It uses the QtQuick qml framework.
QML fundamentals
The definition of QML, Qt, and QtQuick are a bit vague and confusing, so i will try my best to explain it.
What is QML?
QML, or Qt Meta-object Language) is a user interface markup language. I would describe it to be a weird mix of JSON and JavaScript.
QML is made for designing user interfaces on things like an app or desktop UI(user interface).
QML uses declarative syntax, meaning that you describe what you want, not how to do it. It’s reactive, meaning when data changes, the ui changes automatically.
And another big thing is that it’s integrated with JavaScript, so you can embed logic or events inside it.
What is QtQuick?
QtQuick is the framework built on top of Qt (which is a C++ toolkit, utilizing the QML language). It’s the engine that takes your QML code and makes it show up on your screen. Think of QML as the language and QtQuick as the runtime that makes the language do things.