What is the intended design of the emissionPhaseObjectGraphVisitorFactories?

[stijnherreman]

While working on some changes to facilitate #807 and #677 I'm looking into the emissionPhaseObjectGraphVisitorFactories inside the serializer builders. I'm trying to understand the intended design here, but the code is leaving me confused.

There are 4 chained visitors:

• CustomSerializationObjectGraphVisitor (outermost)
  This visitor may write YAML and prevent inner visitors from running in bool Enter().
• AnchorAssigningObjectGraphVisitor
  This visitor may emit events and prevent inner visitors from running in bool Enter(). It also ignores inner visitor implementations of VisitMappingStart(), VisitSequenceStart() and VisitScalar().
• DefaultValuesObjectGraphVisitor
  This visitor may prevent inner visitors from running in bool EnterMapping().
• CommentsObjectGraphVisitor (innermost)
  This visitor may emit events in bool EnterMapping().

I don't understand why the visitors are writing YAML or emiting events in the bool methods. It feels like the visitors must know about the implementation of eachother and their position in the chain, and are forced to incorrectly implement IObjectGraphVisitor to work around the other visitors.

Some of the relevant code traces back to the early days of the library, so maybe the intended design was lost along the way? Can anyone shed some light?