The SEC sets the rules. You can look them up at the SEC site. The main one is what is considered material information. And that MUST be reported in an 8K public disclosure filing.
Form 8-K is used to notify investors of a current event. These types of events include:
Signing, amending or terminating material definitive agreements not made in the ordinary course of business (SUCH AS MANUFACTURING, ASSEMBLING, PATENTS and DISTRIBUTION and SALES)
Bankruptcies or receiverships
Consummation of a material asset acquisition or sale (PATENTS)
Results of operations and financial condition
Creating certain financial obligations, such as incurrence of material debt (WOULD ACCOUNT FOR STOCK ISSUANCES, MANUFACTURING CONTRACTS, COMPONENT ACQUISITIONS, ETC)
Triggering events that accelerate material obligations (such as defaults on a loan)
Layoffs
shutting down a plant (WHEN YOU STOP MANUFACTURING AT ONE LOCATION)
material change in services or outlets (WHEN YOU SIGN A SALES FORCE)
Material impairments (WHEN YOU LOSE A LAWSUIT, GET A CEASE AND DESIST ON PATENT INFRINGEMENT)
Delisting from a securities exchange or failing to satisfy listing requirements
Unregistered equity sales (private placements) (WOULD ACCOUNT FOR INCREASE IN O/S)
Modifications to shareholder rights
Change in accountants
Determinations that previously issued financial statements cannot be relied upon
Change in control
Senior officer appointments and departures
Director elections and departures
Amendments to certificate/articles of incorporation or bylaws
Changes in fiscal year
Trading suspension under employee benefit plans
Amendments or waivers of code of ethics
Changes in shell company status
Results of shareholder votes
Disclosures applicable to issuers of asset-backed securities
Disclosures necessary to comply with Regulation FD
Other material events (ANYTHING THAT HAS A MATERIAL EFFECT such as PATENTS, PRODUCTS, ETC)
Certain financial statements and other exhibits
