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w:rPr direct-property uniqueness
w:rPr (CT_RPr) uses a repeatable property choice, not an ordered child
sequence. Part 1 §17.3.2.28 requires each direct formatting property to occur
at most once. The shared run-property builder keys supported children by local
name, preventing duplicate direct properties. Its stable output order is an
implementation choice, not a conformance claim. Tests assert uniqueness,
exact values, namespace-aware live attributes, and load/save preservation.