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Harper Lee has remained famously detached from interpreting the novel since the mid-1960s. However, she gave some insight into her themes when, in a rare letter to the editor, she wrote in response to the passionate reaction her book caused: "Surely it is plain to the simplest intelligence that To Kill a Mockingbird spells out in words of seldom more than two syllables a code of honor and conduct, Christian in its ethic, that is the heritage of all Southerners."

According to Lee, her book simply expressed a Christian code of honor and conduct inherit to whom?
all Southerners