Share percentage that directors are forced to sell

I read the artile about” read the mind of AFM marker” which refers to the share percentages that directors are forced to sell all the shares that they are currently holding, that is under 10% or other numbers depends on the country’s legislation, to the bidders. I can’t find about that information in BPP Workbook. I want to know more about that matter, where can I find information about that?
Thank you!