/AAA    
/AAA/CCC
/AAA/DDD/BBB
//BBB
//DDD/BBB
/AAA/CCC/DDD/*
/*/*/*/BBB
//*
/AAA/BBB[1]
/AAA/BBB[last()]
//@id
//BBB[@id]
//BBB[@name]
//BBB[@*]
//BBB[not(@*)]
//BBB[@id='b1']
//BBB[@name='bbb']
//BBB[normalize-space(@name)='bbb']
//*[count(BBB)=2]
//*[count(*)=2]
//*[count(*)=3]
//*[name()='BBB']
//*[starts-with(name(),'B')]
//*[contains(name(),'C')]
//*[string-length(name()) = 3]
//*[string-length(name()) < 3]
//*[string-length(name()) > 3]
//CCC | //BBB
/AAA/EEE | //BBB
/AAA/EEE | //DDD/CCC | /AAA | //BBB
/AAA
/child::AAA
/AAA/BBB
/child::AAA/child::BBB
/child::AAA/BBB
/descendant::*
/AAA/BBB/descendant::*
//CCC/descendant::*
//CCC/descendant::DDD
//DDD/parent::*
/AAA/BBB/DDD/CCC/EEE/ancestor::*
//FFF/ancestor::*
/AAA/BBB/following-sibling::*
//CCC/following-sibling::*
/AAA/XXX/preceding-sibling::*
//CCC/preceding-sibling::*
/AAA/XXX/following::*
//ZZZ/following::*
/AAA/XXX/preceding::*
//GGG/preceding::*
/AAA/XXX/descendant-or-self::*
//CCC/descendant-or-self::*
/AAA/XXX/DDD/EEE/ancestor-or-self::*
//GGG/ancestor-or-self::*
//GGG/ancestor::*
//GGG/descendant::*
//GGG/following::*
//GGG/preceding::*
//GGG/self::*
//GGG/ancestor::* | //GGG/descendant::* | //GGG/following::* | //GGG/preceding::* | //GGG/self::*
//BBB[position() mod 2 = 0 ]
//BBB[ position() = floor(last() div 2 + 0.5) or position() = ceiling(last() div 2 + 0.5) ]
//CCC[ position() = floor(last() div 2 + 0.5) or position() = ceiling(last() div 2 + 0.5) ]

You can found more details at here: http://www.cnblogs.com/thinhunan/archive/2006/10/11/525947.html#a9