Axis: preceding-sibling
ElementNode-set
AAA id = a1
BBB id = b1
BBB id = b2b1
AAA id = a2a1
BBB id = b3
BBB id = b4b3
CCC id = c1b3 b4
CCC id = c2
BBB id = b5b3 b4 c1
CCC id = c3