In reply to: It's meant to be a warning, not a punishment posted by wcnitz
After an accumulation of fouls, the referee warns the captain that the next one will result in a player being sent off for 10 minutes. And they are not reluctant to follow through. The next ruck infringement, even if it is minor and by a new player that has not committed fouls before…off he goes for 10 minutes. And everyone accepts this as the proper way to officiate the match.
And the weaker-willed referees at the lower levels. But I make it clear to players I've cautioned that they are on very thin ice, unless the caution was for dissent. In which case, I just expect them to shut up.
But that's a IFAB/FIFA guidance issue along implementation, not the laws themselves. Law 12 doesn't account for what you're referring to.
That's the point of a caution for persistent infringement, right? You break the rules multiple times, you get a caution. At that point you are already persistent, so additional transgressions would be even more persistent.
But there's no 'additionally persistent', and, generally, you'll never see a second yellow for PI because the player had already checked their behavior because of the original caution.