setPropertyFromString possible return values
Iterates the event's properties as strings. Note that keys may be repeated and a get property request may call your sink with null. It it does, it means the key either doesn't request or cannot be represented by json in the current implementation.
Requests a property to be delivered to you as a string, through your sink delegate.
Sets the given property, if it exists, to the given value, if possible. If strIsJson is true, it will json decode (if the implementation wants to) then apply the value, otherwise it will treat it as a plain string.
You can mix this in to get an implementation in child classes. This does getPropertyAsString and getPropertiesList.
You can mix this in to get an implementation in child classes. This does setPropertyFromString.