You can use the keyword question to refer to "the name of the current question", so that, for example, the validation condition
me:value > question(previous)
on a repeating question will fire if you enter a value which is greater than the corresponding value in the previous row. This works for any repeating question which is of type numeric.
A question BPPosition may have a derivation as follows:
case( (question:cycle = 1, 'Standing'), (question:cycle = 2, 'Sitting'), (question:cycle = 3, 'Supine') )
This will display the text Standing, Sitting and Supine in the first three rows of any question group which contains the BPPosition question.
Click here to see another way of deriving text values.