@brief Restricts the last statement in the chain to return
only elements of a specified set of collections

`graph_query.restrict(restrictions)`

By default all collections in the graph are searched for matching elements
whenever vertices and edges are requested.
Using *restrict* after such a statement allows to restrict the search
to a specific set of collections within the graph.
Restriction is only applied to this one part of the query.
It does not effect earlier or later statements.

@PARAMS

@PARAM{restrictions, array, optional}
Define either one or a list of collections in the graph.
Only elements from these collections are taken into account for the result.

@EXAMPLES

Request all directly connected vertices unrestricted:

@EXAMPLE_ARANGOSH_OUTPUT{generalGraphFluentAQLUnrestricted}
  var examples = require("@arangodb/graph-examples/example-graph.js");
  var graph = examples.loadGraph("social");
  var query = graph._vertices({name: "Alice"});
  query.edges().vertices().toArray();
~ examples.dropGraph("social");
@END_EXAMPLE_ARANGOSH_OUTPUT

Apply a restriction to the directly connected vertices:

@EXAMPLE_ARANGOSH_OUTPUT{generalGraphFluentAQLRestricted}
  var examples = require("@arangodb/graph-examples/example-graph.js");
  var graph = examples.loadGraph("social");
  var query = graph._vertices({name: "Alice"});
  query.edges().vertices().restrict("female").toArray();
~ examples.dropGraph("social");
@END_EXAMPLE_ARANGOSH_OUTPUT

Restriction of a query is only valid for collections known to the graph:

@EXAMPLE_ARANGOSH_OUTPUT{generalGraphFluentAQLRestrictedUnknown}
  var examples = require("@arangodb/graph-examples/example-graph.js");
  var graph = examples.loadGraph("social");
  var query = graph._vertices({name: "Alice"});
  query.edges().vertices().restrict(["female", "male", "products"]).toArray(); // xpError(ERROR_BAD_PARAMETER);
~ examples.dropGraph("social");
@END_EXAMPLE_ARANGOSH_OUTPUT