Documentation Conventions reads:

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The documentation convention followed in the major normative clauses of this specification details the normative prescriptive rules in the first subclause and describe the non-normative UBL 2.13 Documents, libraries, components and extensions application of those rules in the second subclause. Where possible, subsequent sub-subclauses under each subclause correspond the NDR rules with the UBL 2.1 application of those rules.
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Just using the heads from section 3, I interpret those conventions to mean:

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3 Documents, libraries, components and extensions [No rules provided for main clauses, that I see anyway.]

3.1 Rules for structuring information bundles [Normative, including any subclauses]

3.2 UBL structuring of information bundles (Non-Normative) [Non-normative and labeled as non-normative]
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The main clauses not having normative or non-normative status is a serious problem. I won't file a separate issue but note all the main clauses are also hanging paragraphs in the ISO sense. Rather than relying on readers to remember the subclause 1 versus subclause 2 distinction, wouldn't it be simpler to label the main subclauses?