Thank you @shreedhar for your answer.
It made me recall a comment from a frequent and heavy user of Photoshop I once read. He wrote something like this: One of the lessons I have learned over the years is that you can achieve almost the same result by different routes, that is using different tools in different combinations. You are more or less expressing the same and it’s of course true.
How do you go about becoming an experienced and skilful user of RT? RT is not easy to master, I think. You have to put a lot of effort into it and in many cases the documentation is not easy to fully understand. This is also apparent from reading the posts in the forum. You also miss all the books, articles, youtube videos and all the stuff you can Google in the Photoshop (Elements) world.
So you have to edit a lot of photos and try out the different tools. The photo in question was taken specifically to test the Retinex tool which was, and still is, somewhat of a mystery to me. Earlier this year I tried to translate the French documentation into English using Google. The result was “interesting” and not that helpful! Now the documentation is in English and I decided to have another go at Retinex.
I’m still more or less left with the question: What are the best qualities of Retinex? When should I go for Retinex as my first choice editing a photo taking into consideration that one has only limited time to tune each photo?