"Jem rose and broke the remaining code of our childhood." What new violation causes Scout to make this comment in To Kill a Mockingbird?

This quotation actually can be found in Chapter 14 (rather
than Chapter 12) of To Kill a Mockingbird. Jem and Scout had just
gotten into a fist fight earlier in the evening. Jem had threatened to "spank" his
sister, so, after calling him a "damn morphodite," Scout went on the attack. It took
Atticus to break them up and send them to bed. But shortly afterward, Dill suddenly
appeared from under Scout's bed. He had run away from home and hoped to hide out in
Scout's room for a while. But Jem knew that Dill's parents would be worried, so he
decided to break "the remaining code of our childhood": He ratted Dill out to Atticus.
But it was all for the best, as Jem knew it would be. Atticus broke the news gently to
Dill's Aunt Rachel, and Dill got to spend the rest of the night in the Finches'
house--and what must have been an interesting night sharing the bed with
Scout!