2.1.1429 Part 1 Section 21.2.2.3, applyToSides (Apply To Sides)
a. The standard states that the applyToSides element specifies that the picture shall be applied to the sides of the point or series.
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In Office this element also specifies that the picture shall be applied to the floor or the side wall but is ignored on the back wall of a 3D chart.