a MutationOperation for a set of mutations related to a particular
element
The handler could be invoked multiple times in each "round" (cycle of event
loop) if there are mutation operations for more than one element that match
the supplied OnMutationOptions.
The handler is invoked with one argument:
The handler could be invoked multiple times in each "round" (cycle of event loop) if there are mutation operations for more than one element that match the supplied OnMutationOptions.