Restrict what can be dropped on app instances. Accepting means allowing a file to be dropped into an instance.
One of the following file types must be used with an .Accept file:
A gallery app may want to disallow dropping anything but images into it. A 2-column splitter app may only want to accept anything that can be inlined into a web page.
The .Accept file allows you to set these restrictions.
If the .Accept file does not exist, the app will default to not accept anything.