Referring to the toy example from the article: Without »weak« purity, renderScene() could not be pure at all, but now, it can even be »strongly« so. The point

Referring to the toy example from the article: Without »weak« purity, renderScene() could not be pure at all, but now, it can even be »strongly« so. The point is that it enables some function to be pure in the traditional sense even if their implementation relies on mutating data – any idea how I could make this more clear?