Hello! Can someone clarify what the sentence means:
“If one margin is negative, its value will be subtracted from the total.”
Total from what?
Hi @martinteam and welcome to the community 
Sorry for the long delay.
This should read “If one margin is negative, its value will be subtracted from the positive margin”. So when one margin is 50px and the other one is -40px they’ll collapse to an 10px margin.
At the bottom of the article is a box where you can report this issue if you like.
Have a nice day,
Michael