I had to laugh when reading the first part of this manuel intended for the interpretation of the words of Archbishop Lefebvre in favor of a reconciliation with Rome.
If these rules of interpretation had been applied to the recent words of Benedict XVI concerning restoration, surely Tradition would not mistake them for their Master's voice.
A Few Sensible Rules: by Fr. Celier, SSPX, Part I
"Therefore, if some expressions, some statements penned by an author seem out of tune, then one ought a priori, unless there is a well-founded reason, to reconcile them with the recurring expressions and constant statements of that author. Ordinarily, indeed, it is methodologically sound to interpret what is variable in terms of what is constant, the obscure by what is clear, novel language in terms of oft-repeated thinking, and not vice versa. Obviously this is not a question of rejecting altogether any development of a personís thought: it is, instead, a matter of not interpreting a simple variation in vocabulary as a break with a whole body of thought that has been clearly and constantly affirmed.
Moreover, when the author carries out responsibilities, especially when he holds a position of authority, it is legitimate and necessary to understand his words in the light of his actions, and his actions in the light of his words. If an author has occasionally uttered some more or less ambiguous words that can be interpreted in favor of a thesis, but in carrying out his responsibilities he has systematically removed defenders of that thesis, then it is methodologically unsound to understand those ambiguous words as though they in fact approved the aforesaid thesis."