2.1.1760 Part 4 Section 14.4.3, left (Table Cell Leading Margin Exception)

a.   The standard specifies this additional element, semantically equivalent to the start element ("[ISO/IEC-29500-1] §17.4.35; start").

Word ignores this element if the start element ("[ISO/IEC-29500-1] §17.4.35; start") is present as a sibling.