Issue #2910181 by sarvjeetsingh, anmolgoyal74, apaderno, pameeela, jcalais:...

 * "realms". In hook_node_access_records(), the realms and grant IDs are

 * associated with permission to view, edit, and delete individual nodes.

 *

 * The realms and grant IDs can be arbitrarily defined by your node access

 * module; it is common to use role IDs as grant IDs, but that is not required.

 * Your module could instead maintain its own list of users, where each list has

 * an ID. In that case, the return value of this hook would be an array of the

 * list IDs that this user is a member of.

 * Grant IDs can be arbitrarily defined by a node access module using a list of

 * integer IDs associated with users.

 *

 * A node access module may implement as many realms as necessary to properly

 * define the access privileges for the nodes. Note that the system makes no