What principles did Jesus advocate when it came to interpreting the Torah and giving rulings based on it?

On one hand, he seems to suggest that the quality of actions and of the mind, regardless of commandments in the Torah, are the measure: e.g. But those things which proceed out of the mouth come forth from the heart; and they defile the man.

He never says how far this can be extended - could, e.g. sexual morals be interpreted by this method? (It's not the kind of sex or the kind of partner, it's to what purpose or whatever?) Where's the demarcation line for how far this method can be extended?

Whence does the principle in Matthew 19, "Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder." Can this be extended to What God has made X, let not man make un-X? Can it be extended to what God has forbidden, man cannot permit? What God has permitted, man cannot forbid?

I should reread the entire gospels, I am kind of certain there's one more principle there, but it wasn't present in matthew. So, rereading them before the next post.