2.1.1691 Part 1 Section 22.1.2.84, pos (Position)

a.   The standard states that the pos element specifies the position of the bar in the bar object.

Word uses the pos element to specify the position of the bar in the bar object or the position of the character in the groupChr object.

b.   The standard states that the default value for position of the bar in the bar object is top.

Office implements the default value for the position of the bar in the bar object as bot.