InfoPath Dev

 The expense report template for Infopath that can be downloaded from Microsoft has a command button at the end of each line item. Upon clicking this button it displays an optional section for the line item based on the category chosen.

 There is a rule on the button that i cant work out what it does

Action - Set a fields value

Field - itemPosition

Value: count(preceding-sibling::*)

The part that i haven't encountered before is the preceding and sibling functions mentioned in the value section.

 What does this mean and how does it enable the optional section on the form when the button is clicked? There isn't any code anywhere that i can find

the Itemized Expenses is a repeating table

and the Item Details is a repeating section.

item details has a conditional formatting that forces it to show only the section number that equals the number in the itemposition.

when you click the button, it sets the value of itemposition to the previous row # of the repeating table you are in

function count(preceding-sibling::*) gives the previous row/section #