Update List x Using the Elements of List new.x.
Details
This function updates list x by name. An element of new.x that is
itself a named list is merged into the matching element of x the same
way, by name. An element that is a list without names, such as a
multilayer() object, has no names to merge by, so it replaces the
matching element of x whole. If a function is provided to replace an
element that was originally not a function, this function will be applied
to the original value.