Keywords: Unity, UIElements, GUI, UI

Docs

UIElements Developer Guide
https://docs.unity3d.com/Manual/UIElements.html

UIElements Developer Guide
https://docs.unity3d.com/2018.3/Documentation/Manual/UIElements.html

Runtime dev UI Runtime game UI Editor
IMGUI for debugging not recommmended ✅
UGUI ✅ ✅ ⬜️
UIElements 2019.x 2020.x 2019.1
Blogs

What’s new with UIElements in 2019.1
https://blogs.unity3d.com/2019/04/23/whats-new-with-uielements-in-2019-1/

Evolving the Unity Editor UX
https://blogs.unity3d.com/2019/08/29/evolving-the-unity-editor-ux/

Youtube Tutorials

Customize the Unity Editor with UIElements!
https://www.youtube.com/watch?v=CZ39btQ0XlE
UIElementsDemo
https://oc.unity3d.com/index.php/s/F3J0eqPz3ls7z5l

Building UI for games with the new UI Builder - Unite Copenhagen
https://www.youtube.com/watch?v=t4tfgI1XvGs

Sources

Unity project containing examples to use UIElements in the Editor
https://github.com/Unity-Technologies/UIElementsExamples

Usage

How to create UIElements Editor Window?

How to change pivot of UI elements

Can’t change the pivot of a UI element
https://answers.unity.com/questions/871238/cant-change-the-pivot-of-a-ui-element.html

How to change Rect Transform of UI elements

How To Overwrite Width And Height Values That Are Driven By A Layout Group In Runtime.
https://support.unity3d.com/hc/en-us/articles/115000179163-How-to-overwrite-Width-and-Height-values-that-are-driven-by-a-Layout-Group-in-runtime-

I'm not upset that you lied to me, I'm upset that from now on I can't believe you. ― Friedrich Nietzsche