Select Effect Layer. Selects an effect layer and starts a new layer segment in the request string, which is associated with the current layer.
Effect layer number (int not equal to 0).
All commands within the new segment are applied to the specified effect layer. An effect layer segment is terminated by the next
effect= command or by the end of the request.
n must be less than 0 for outer layer effects (i.e. effects behind the parent layer) and greater than 0 for inner layer effects (i.e. effects within the parent layer). Effect layer numbers do not have to be consecutive.
The effect layer number specifies the z-order, in case of multiple effect layers for the same parent layer. Higher-numbered layers are placed on top of lower-numbered layers.
Effect layers may be attached to
Effect layer command.
n must not be 0.