XPath手册

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[[注:]本手册由ZVON版本加工而成,对JQuery感兴趣的朋友可以看一下源代码]

页首
  • /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) ]
基本的XPath语法类似于在一个文件系统中定位文件,如果路径以斜线 / 开始, 那么该路径就表示到一个元素的绝对路径
/AAA选择根元素AAA
     <AAA
          <BBB/> 
          <CCC/> 
          <BBB/> 
          <BBB/> 
          <DDD
               <BBB/> 
          </DDD
          <CCC/> 
     </AAA>回页首/AAA/CCC选择AAA的所有CCC子元素
     <AAA
          <BBB/> 
          <CCC/> 
          <BBB/> 
          <BBB/> 
          <DDD
               <BBB/> 
          </DDD
          <CCC/> 
     </AAA>回页首/AAA/DDD/BBB选择AAA的子元素DDD的所有子元素
     <AAA
          <BBB/> 
          <CCC/> 
          <BBB/> 
          <BBB/> 
          <DDD
               <BBB/> 
          </DDD
          <CCC/> 
     </AAA>回页首
如果路径以双斜线 // 开头, 则表示选择文档中所有满足双斜线//之后规则的元素(无论层级关系)
//BBB选择所有BBB元素
     <AAA
          <BBB/> 
          <CCC/> 
          <BBB/> 
          <DDD
               <BBB/> 
          </DDD
          <CCC
               <DDD
                    <BBB/> 
                    <BBB/> 
               </DDD
          </CCC
     </AAA>回页首//DDD/BBB选择所有父元素是DDD的BBB元素
     <AAA
          <BBB/> 
          <CCC/> 
          <BBB/> 
          <DDD
               <BBB/> 
          </DDD
          <CCC
               <DDD
                    <BBB/> 
                    <BBB/> 
               </DDD
          </CCC
     </AAA>回页首
星号 * 表示选择所有由星号之前的路径所定位的元素
/AAA/CCC/DDD/*选择所有路径依附于/AAA/CCC/DDD的元素
     <AAA
          <XXX
               <DDD
                    <BBB/> 
                    <BBB/> 
                    <EEE/> 
                    <FFF/> 
               </DDD
          </XXX
          <CCC
               <DDD
                    <BBB/> 
                    <BBB/> 
                    <EEE/> 
                    <FFF/> 
               </DDD
          </CCC
          <CCC
               <BBB
                    <BBB
                         <BBB/> 
                    </BBB
               </BBB
          </CCC
     </AAA>回页首/*/*/*/BBB选择所有的有3个祖先元素的BBB元素
     <AAA
          <XXX
               <DDD
                    <BBB/> 
                    <BBB/> 
                    <EEE/> 
                    <FFF/> 
               </DDD
          </XXX
          <CCC
               <DDD
                    <BBB/> 
                    <BBB/> 
                    <EEE/> 
                    <FFF/> 
               </DDD
          </CCC
          <CCC
               <BBB
                    <BBB
                         <BBB/> 
                    </BBB
               </BBB
          </CCC
     </AAA>回页首//*选择所有元素
     <AAA
          <XXX
               <DDD
                    <BBB/> 
                    <BBB/> 
                    <EEE/> 
                    <FFF/> 
               </DDD
          </XXX
          <CCC
               <DDD
                    <BBB/> 
                    <BBB/> 
                    <EEE/> 
                    <FFF/> 
               </DDD
          </CCC
          <CCC
               <BBB
                    <BBB
                         <BBB/> 
                    </BBB
               </BBB
          </CCC
     </AAA>回页首
方块号里的表达式可以进一步的指定元素, 其中数字表示元素在选择集里的位置, 而last()函数则表示选择集中的最后一个元素.
/AAA/BBB[1]选择AAA的第一个BBB子元素
     <AAA
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
     </AAA>回页首/AAA/BBB[last()]选择AAA的最后一个BBB子元素
     <AAA
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
     </AAA>回页首//@id选择所有的id属性
     <AAA
          <BBB id = "b1"/> 
          <BBB id = "b2"/> 
          <BBB name = "bbb"/> 
          <BBB/> 
     </AAA>回页首//BBB[@id]选择有id属性的BBB元素
     <AAA
          <BBB id = "b1"/> 
          <BBB id = "b2"/> 
          <BBB name = "bbb"/> 
          <BBB/> 
     </AAA>回页首//BBB[@name]选择有name属性的BBB元素
     <AAA
          <BBB id = "b1"/> 
          <BBB id = "b2"/> 
          <BBB name = "bbb"/> 
          <BBB/> 
     </AAA>回页首//BBB[@*]选择有任意属性的BBB元素
     <AAA
          <BBB id = "b1"/> 
          <BBB id = "b2"/> 
          <BBB name = "bbb"/> 
          <BBB/> 
     </AAA>回页首//BBB[not(@*)]选择没有属性的BBB元素
     <AAA
          <BBB id = "b1"/> 
          <BBB id = "b2"/> 
          <BBB name = "bbb"/> 
          <BBB/> 
     </AAA>回页首
属性的值可以被用来作为选择的准则, normalize-space函数删除了前部和尾部的空格, 并且把连续的空格串替换为一个单一的空格
//BBB[@id='b1']选择含有属性id且其值为'b1'的BBB元素
     <AAA
          <BBB id = "b1"/> 
          <BBB name = " bbb "/> 
          <BBB name = "bbb"/> 
     </AAA>回页首//BBB[@name='bbb']选择含有属性name且其值为'bbb'的BBB元素
     <AAA
          <BBB id = "b1"/> 
          <BBB name = " bbb "/> 
          <BBB name = "bbb"/> 
     </AAA>回页首//BBB[normalize-space(@name)='bbb']选择含有属性name且其值(在用normalize-space函数去掉前后空格后)为'bbb'的BBB元素
     <AAA
          <BBB id = "b1"/> 
          <BBB name = " bbb "/> 
          <BBB name = "bbb"/> 
     </AAA>回页首
count()函数可以计数所选元素的个数
//*[count(BBB)=2]选择含有2个BBB子元素的元素
     <AAA
          <CCC
               <BBB/> 
               <BBB/> 
               <BBB/> 
          </CCC
          <DDD
               <BBB/> 
               <BBB/> 
          </DDD
          <EEE
               <CCC/> 
               <DDD/> 
          </EEE
     </AAA>回页首//*[count(*)=2]选择含有2个子元素的元素
     <AAA
          <CCC
               <BBB/> 
               <BBB/> 
               <BBB/> 
          </CCC
          <DDD
               <BBB/> 
               <BBB/> 
          </DDD
          <EEE
               <CCC/> 
               <DDD/> 
          </EEE
     </AAA>回页首//*[count(*)=3]选择含有3个子元素的元素
     <AAA
          <CCC
               <BBB/> 
               <BBB/> 
               <BBB/> 
          </CCC
          <DDD
               <BBB/> 
               <BBB/> 
          </DDD
          <EEE
               <CCC/> 
               <DDD/> 
          </EEE
     </AAA>回页首
name()函数返回元素的名称, start-with()函数在该函数的第一个参数字符串是以第二个参数字符开始的情况返回true, contains()函数当其第一个字符串参数包含有第二个字符串参数时返回true.
//*[name()='BBB']选择所有名称为BBB的元素(这里等价于//BBB)
     <AAA
          <BCC
               <BBB/> 
               <BBB/> 
               <BBB/> 
          </BCC
          <DDB
               <BBB/> 
               <BBB/> 
          </DDB
          <BEC
               <CCC/> 
               <DBD/> 
          </BEC
     </AAA>回页首//*[starts-with(name(),'B')]选择所有名称以"B"起始的元素
     <AAA
          <BCC
               <BBB/> 
               <BBB/> 
               <BBB/> 
          </BCC
          <DDB
               <BBB/> 
               <BBB/> 
          </DDB
          <BEC
               <CCC/> 
               <DBD/> 
          </BEC
     </AAA>回页首//*[contains(name(),'C')]选择所有名称包含"C"的元素
     <AAA
          <BCC
               <BBB/> 
               <BBB/> 
               <BBB/> 
          </BCC
          <DDB
               <BBB/> 
               <BBB/> 
          </DDB
          <BEC
               <CCC/> 
               <DBD/> 
          </BEC
     </AAA>回页首
string-length函数返回字符串的字符数,你应该用&lt;替代<, 用&gt;代替>
//*[string-length(name()) = 3]选择名字长度为3的元素
     <AAA
          <Q/> 
          <SSSS/> 
          <BB/> 
          <CCC/> 
          <DDDDDDDD/> 
          <EEEE/> 
     </AAA>回页首//*[string-length(name()) < 3]选择名字长度小于3的元素
     <AAA
          <Q/> 
          <SSSS/> 
          <BB/> 
          <CCC/> 
          <DDDDDDDD/> 
          <EEEE/> 
     </AAA>回页首//*[string-length(name()) > 3]选择名字长度大于3的元素
     <AAA
          <Q/> 
          <SSSS/> 
          <BB/> 
          <CCC/> 
          <DDDDDDDD/> 
          <EEEE/> 
     </AAA>回页首
多个路径可以用分隔符 | 合并在一起
//CCC | //BBB选择所有的CCC和BBB元素
     <AAA
          <BBB/> 
          <CCC/> 
          <DDD
               <CCC/> 
          </DDD
          <EEE/> 
     </AAA>回页首/AAA/EEE | //BBB选择所有的BBB元素和所有是AAA的子元素的EEE元素
     <AAA
          <BBB/> 
          <CCC/> 
          <DDD
               <CCC/> 
          </DDD
          <EEE/> 
     </AAA>回页首/AAA/EEE | //DDD/CCC | /AAA | //BBB可以合并的路径数目没有限制
     <AAA
          <BBB/> 
          <CCC/> 
          <DDD
               <CCC/> 
          </DDD
          <EEE/> 
     </AAA>回页首
child轴(axis)包含上下文节点的子元素, 作为默认的轴,可以忽略不写.
/AAA等价于 /child::AAA
     <AAA
          <BBB/> 
          <CCC/> 
     </AAA>回页首/child::AAA等价于/AAA
     <AAA
          <BBB/> 
          <CCC/> 
     </AAA>回页首/AAA/BBB等价于/child::AAA/child::BBB
     <AAA
          <BBB/> 
          <CCC/> 
     </AAA>回页首/child::AAA/child::BBB等价于/AAA/BBB
     <AAA
          <BBB/> 
          <CCC/> 
     </AAA>回页首/child::AAA/BBB二者都可以被合并
     <AAA
          <BBB/> 
          <CCC/> 
     </AAA>回页首
descendant (后代)轴包含上下文节点的后代,一个后代是指子节点或者子节点的子节点等等, 因此descendant轴不会包含属性和命名空间节点.
/descendant::*选择文档根元素的所有后代.即所有的元素被选择
     <AAA
          <BBB
               <DDD
                    <CCC
                         <DDD/> 
                         <EEE/> 
                    </CCC
               </DDD
          </BBB
          <CCC
               <DDD
                    <EEE
                         <DDD
                              <FFF/> 
                         </DDD
                    </EEE
               </DDD
          </CCC
     </AAA>回页首/AAA/BBB/descendant::*选择/AAA/BBB的所有后代元素
     <AAA
          <BBB
               <DDD
                    <CCC
                         <DDD/> 
                         <EEE/> 
                    </CCC
               </DDD
          </BBB
          <CCC
               <DDD
                    <EEE
                         <DDD
                              <FFF/> 
                         </DDD
                    </EEE
               </DDD
          </CCC
     </AAA>回页首//CCC/descendant::*选择在祖先元素中有CCC的所有元素
     <AAA
          <BBB
               <DDD
                    <CCC
                         <DDD/> 
                         <EEE/> 
                    </CCC
               </DDD
          </BBB
          <CCC
               <DDD
                    <EEE
                         <DDD
                              <FFF/> 
                         </DDD
                    </EEE
               </DDD
          </CCC
     </AAA>回页首//CCC/descendant::DDD选择所有以CCC为祖先元素的DDD元素
     <AAA
          <BBB
               <DDD
                    <CCC
                         <DDD/> 
                         <EEE/> 
                    </CCC
               </DDD
          </BBB
          <CCC
               <DDD
                    <EEE
                         <DDD
                              <FFF/> 
                         </DDD
                    </EEE
               </DDD
          </CCC
     </AAA>回页首
parent轴(axis)包含上下文节点的父节点, 如果有父节点的话
//DDD/parent::*选择DDD元素的所有父节点
     <AAA
          <BBB
               <DDD
                    <CCC
                         <DDD/> 
                         <EEE/> 
                    </CCC
               </DDD
          </BBB
          <CCC
               <DDD
                    <EEE
                         <DDD
                              <FFF/> 
                         </DDD
                    </EEE
               </DDD
          </CCC
     </AAA>回页首
ancestor轴(axis)包含上下节点的祖先节点, 该祖先节点由其上下文节点的父节点以及父节点的父节点等等诸如此类的节点构成,所以ancestor轴总是包含有根节点,除非上下文节点就是根节点本身.
/AAA/BBB/DDD/CCC/EEE/ancestor::*选择一个绝对路径上的所有节点
     <AAA
          <BBB
               <DDD
                    <CCC
                         <DDD/> 
                         <EEE/> 
                    </CCC
               </DDD
          </BBB
          <CCC
               <DDD
                    <EEE
                         <DDD
                              <FFF/> 
                         </DDD
                    </EEE
               </DDD
          </CCC
     </AAA>回页首//FFF/ancestor::*选择FFF元素的祖先节点
     <AAA
          <BBB
               <DDD
                    <CCC
                         <DDD/> 
                         <EEE/> 
                    </CCC
               </DDD
          </BBB
          <CCC
               <DDD
                    <EEE
                         <DDD
                              <FFF/> 
                         </DDD
                    </EEE
               </DDD
          </CCC
     </AAA>回页首
following-sibling轴(axis)包含上下文节点之后的所有兄弟节点
/AAA/BBB/following-sibling::* 
     <AAA
          <BBB
               <CCC/> 
               <DDD/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//CCC/following-sibling::* 
     <AAA
          <BBB
               <CCC/> 
               <DDD/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首
preceding-sibling 轴(axis)包含上下文节点之前的所有兄弟节点
/AAA/XXX/preceding-sibling::* 
     <AAA
          <BBB
               <CCC/> 
               <DDD/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//CCC/preceding-sibling::* 
     <AAA
          <BBB
               <CCC/> 
               <DDD/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首
following轴(axis)包含同一文档中按文档顺序位于上下文节点之后的所有节点, 除了祖先节点,属性节点和命名空间节点
/AAA/XXX/following::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ
                    <DDD/> 
                    <DDD
                         <EEE/> 
                    </DDD
               </ZZZ
               <FFF
                    <GGG/> 
               </FFF
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//ZZZ/following::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ
                    <DDD/> 
                    <DDD
                         <EEE/> 
                    </DDD
               </ZZZ
               <FFF
                    <GGG/> 
               </FFF
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首
following轴(axis)包含同一文档中按文档顺序位于上下文节点之前的所有节点, 除了祖先节点,属性节点和命名空间节点
/AAA/XXX/preceding::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ
                    <DDD/> 
               </ZZZ
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//GGG/preceding::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ
                    <DDD/> 
               </ZZZ
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首
descendant-or-self 轴(axis)包含上下文节点本身和该节点的后代节点
/AAA/XXX/descendant-or-self::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ
                    <DDD/> 
               </ZZZ
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//CCC/descendant-or-self::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ
                    <DDD/> 
               </ZZZ
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首
ancestor-or-self 轴(axis)包含上下文节点本身和该节点的祖先节点
/AAA/XXX/DDD/EEE/ancestor-or-self::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ
                    <DDD/> 
               </ZZZ
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//GGG/ancestor-or-self::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ
                    <DDD/> 
               </ZZZ
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <DDD/> 
                    <CCC/> 
                    <FFF/> 
                    <FFF
                         <GGG/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首
ancestor, descendant, following, preceding 和self轴(axis)分割了XML文档(忽略属性节点和命名空间节点), 不能交迭, 而一起使用则包含所有节点
//GGG/ancestor::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <FFF
                         <HHH/> 
                         <GGG
                              <JJJ
                                   <QQQ/> 
                              </JJJ
                              <JJJ/> 
                         </GGG
                         <HHH/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//GGG/descendant::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <FFF
                         <HHH/> 
                         <GGG
                              <JJJ
                                   <QQQ/> 
                              </JJJ
                              <JJJ/> 
                         </GGG
                         <HHH/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//GGG/following::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <FFF
                         <HHH/> 
                         <GGG
                              <JJJ
                                   <QQQ/> 
                              </JJJ
                              <JJJ/> 
                         </GGG
                         <HHH/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//GGG/preceding::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <FFF
                         <HHH/> 
                         <GGG
                              <JJJ
                                   <QQQ/> 
                              </JJJ
                              <JJJ/> 
                         </GGG
                         <HHH/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//GGG/self::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <FFF
                         <HHH/> 
                         <GGG
                              <JJJ
                                   <QQQ/> 
                              </JJJ
                              <JJJ/> 
                         </GGG
                         <HHH/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首//GGG/ancestor::* | //GGG/descendant::* | //GGG/following::* | //GGG/preceding::* | //GGG/self::* 
     <AAA
          <BBB
               <CCC/> 
               <ZZZ/> 
          </BBB
          <XXX
               <DDD
                    <EEE/> 
                    <FFF
                         <HHH/> 
                         <GGG
                              <JJJ
                                   <QQQ/> 
                              </JJJ
                              <JJJ/> 
                         </GGG
                         <HHH/> 
                    </FFF
               </DDD
          </XXX
          <CCC
               <DDD/> 
          </CCC
     </AAA>回页首
div运算符做浮点除法运算, mod运算符做求余运算, floor函数返回不大于参数的最大整数(趋近于正无穷), ceiling返回不小于参数的最小整数(趋近于负无穷)
//BBB[position() mod 2 = 0 ]选择偶数位置的BBB元素
     <AAA
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <CCC/> 
          <CCC/> 
          <CCC/> 
     </AAA>回页首//BBB[ position() = floor(last() div 2 + 0.5) or position() = ceiling(last() div 2 + 0.5) ]选择中间的BBB元素
     <AAA
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <CCC/> 
          <CCC/> 
          <CCC/> 
     </AAA>回页首//CCC[ position() = floor(last() div 2 + 0.5) or position() = ceiling(last() div 2 + 0.5) ]选择中间的CCC元素
     <AAA
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <BBB/> 
          <CCC/> 
          <CCC/> 
          <CCC/> 
     </AAA>回页首
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