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http://heycam.github.io/webidl/#dfn-iterator-return-no-value [[ not return a value ]] This is latter referred to as "no value" and those links are broken somehow. Also, it should be made clear that this is something that needs to be returned from the "iterator behavior". (Is that not more like an iterator algorithm or is "behavior" the term IDL uses for algorithm?)
I can no longer find this text in the current iteration of the iterator spec, so, probably fixed?