2.1.1705 Part 1 Section 22.1.2.111, sty (style)

a.   The standard says that style is used to map ASCII values to the appropriate Unicode range.

Word uses the style and script to map Unicode values to Math Alphanumeric Unicode values.

b.   The standard implies that the val attribute is optional.

Word requires this attribute.

c.   The standard does not specify a default value for sty.

In Word, the default value for sty is italic.