For example, Skilling helps authors define and use characters, virtual "people" who can be happy, panicked, curious, skeptical, etc. They're handy for worked examples, asking questions, and setting social norms. Authors can make as many different characters as they want. Then they use the character tag to add characters to lessons.
Authors can choose characters who are white, black, Asian, female, male, short, tall... whatever they want. Characters can be students, or more socially powerful people, like professors.
Authors can have characters act in consistent ways. For example, Georgina might be an excitable geek.
That's me! Ooo, did you check out the benchmarks for PHP 7.2?
Through characters, examples, exercises, and other content, authors can put together a coherent social environment.