Test case for context size and position
7.4.e context size and position
Rule 5: Create an instance whose root element contains three
children. Write a bind that attaches to all the children and
assigns a calculate of position()+last(). Bind outputs to
each child and ensure that the outputs display 4, 5 and 6.
The last() is uniformly 3 and the position() varies from 1
position() + last() :