Firstly, this looks fantastic. And the GUI not taking over the main loop is a wonderful feature. This is something that has really irritated me using most other GUI libraries (including Qt).

> The GUI should be declared in C++ code.

While I love the declarative aspect of the above, would the authors consider using a different DDL for layouts rather than C++?

The reason I ask is: this now enables creation of wrappers around this library for other languages like Golang and Python.

Also, having the layouts described as plain data rather than C++ code would allow not having to compile for minor UI/layout changes. Which will in turn permit faster prototyping during UI development.