Returns a special value that can be used with set(), create() or update()
that tells the server to remove the given elements from any array value
that already exists on the server. All instances of each element specified
will be removed from the array. If the field being modified is not already
an array it will be overwritten with an empty array.
Returns a special value that can be used with set(), create() or update()
that tells the server to union the given elements with any array value that
already exists on the server. Each specified element that doesn't already
exist in the array will be added to the end. If the field being modified is
not already an array it will be overwritten with an array containing
exactly the specified elements.
Returns a special value that can be used with set(), create() or update()
that tells the server to increment the the field's current value by the
given value.