Axis: preceding-sibling
Element
Node-set
AAA id = a1
BBB id = b1
BBB id = b2
b1
AAA id = a2
a1
BBB id = b3
BBB id = b4
b3
CCC id = c1
b3 b4
CCC id = c2
BBB id = b5
b3 b4 c1
CCC id = c3