Let's assume an investor wants to buy 20% of the market cap of a small-cap stock valued at $100M.
The investor is a UNWI placing the order (or hundreds of orders over 12 months) through either an online broker or a private bank brokerage service.
Is this usually legal across most exchanges/countries? What is the max % of a market cap a single entity or individual can purchase without having to file any documents or go through a regulatory process? Are there any differences in treatment between an individual, professional and institutional investor? If the investor might also be a family office using the prime brokerage relationship to pass these orders, does this change the process?