Context: After the preamble comes numbered articles, which contain the substance of the parties' actual agreement. Each article heading usually encompasses a paragraph. A long treaty may further group articles under chapter headings.

Question: What follows the preamble in a treaty?
Answer: numbered articles

Question: What is contained in the numbered articles of a treaty?
Answer: the substance of the parties' actual agreement

Question: What does each article heading usually encompass?
Answer: a paragraph

Question: How might the articles in a long treaty be grouped?
Answer: under chapter headings

Question: The numbered articles of a treaty may be grouped by chapter heading in what kind of treaty?
Answer: A long treaty