2.1.1856 Part 4 Section 220.127.116.11, r (Run)
a. The standard allows bold and italic to be set in a math run in the rPr of both Math and WordprocessingML.
If Word reads a math run where bold or italic properties are set in the rPr of WordprocessingML, it ignores those properties during display but then moves them into the Math rPr on save.
b. The standard allows br elements inside a math object.
Word does not allow br elements inside a math object.
c. The standard allows cr elements as a child of a math run.
Word does not allow the cr element inside a math run.
d. The standard allows tab elements as a child of a math run.
Word ignores a tab element if it occurs inside a math run.