When a 2/3rd vote is required

I admit not all parliamentarians are created equal! The 2/3rds vote issue I asked about recently is right there in the book; all I needed to do was spend more time leafing through. A two-thirds vote is required in some instances-"in keeping with accepted parliamentary procedure". "At a meeting where a quorum is present, it takes two-thirds of those voting in the affirmative to adopt a motion. Those who abstain are not counted." Then Robert's lists procedures requiring the 2/3rds vote.