-|@exists@|string|Test if a subproperty is present.|@["properties","exists","my_subproperty"]@|
-
-h4(#filterexpression). Filtering using boolean expressions
-
-In place of an attribute, the first element of the three-element filter array can be a boolean expression. The following restrictions apply:
-* The expression must contain exactly one operator.
-* The operator must be @=@, @<@, @<=@, @>@, or @>=@.
-* There must be exactly one pair of parentheses, surrounding the entire expression.
-* Each operand must be the name of a numeric attribute like @replication_desired@ (literal values like @3@ and non-numeric attributes like @uuid@ are not accepted).
-* The expression must not contain whitespace other than an ASCII space (newline and tab characters are not accepted).
-* The second and third elements of the filter array must be @"="@ and @true@ respectively.
-
-Examples:
-* @["(replication_desired < replication_confirmed)", "=", true]@
-* @["(replication_desired = replication_confirmed)", "=", true]@
+|@exists@|string|Presence of subproperty|@["properties","exists","my_subproperty"]@|
+|@contains@|string, array of strings|Presence of one or more keys or array elements|@["storage_classes_desired", "contains", ["foo", "bar"]]@ (matches both @["foo", "bar"]@ and @["foo", "bar", "baz"]@)
+(note @[..., "contains", "foo"]@ is also accepted, and is equivalent to @[..., "contains", ["foo"]]@)|