We need:

• for system (indexing field ?) criteria
  • site (string) : to restrict search to site(s)
  • page (string): to restrict search to sub-sitemap
  • tag (string): to search by content tags
  • orphan (string or boolean ?): to restrict search to orphan or non-orphan contents
  • shared (boolean): to restrict search to contents which can be shared
  • langContext ? with values all / others / current

• for column criteria
  • site (string) : the content site's name
  • orphan (boolean)
  • shared (boolean)