Artifact Validation Policy properties are not clear

The publib help for artifact validation policy is not clear. It does not describe the kind of things that can be checked... We can check the format of an artifact. There is nothing to guide as to what can be put in the "value" field. File Extension is inadequate as a spreadsheet can have (ods, xls, xlsx, xml, and probably many others). Can you help me understand what "Format of" is, and how to use it? Also how to configure Extension if we want to give more than one extension.

Regards,
Payal