具有层次结构中可选元素的XPath [英] XPath with optional element in hierarchy

问题描述

正如堆栈溢出答案想象你需要选择一个特定的表格，然后选择它的所有行。由于HTML的宽容性，以下三种都是合法标记：

 < table id =foo> < TR> ...< / TR>< /表> 
< table id =foo>< tbody>< tr> ...< / tr>< / tbody>< / table> 
< table id =foo>< tr> ...< / tr>< tbody>< tr> ...< / tr>< / tbody>< /表> 
  

您担心嵌套在表中的表，因此不想使用像< br>
表格[@ id =foo] // tr 。

将你想要的XPath指定为正则表达式，它可能看起来像这样：

table [@ id =foo]（/ tbody）？/ tr

一般来说，如何指定允许选择器层次结构中可选元素的XPath表达式？

<为了说清楚，我并没有试图解决现实世界的问题，或者选择特定文档的特定元素。我正在寻求解决一类问题的技巧。

我不明白你为什么可以这样做。 't use this：

  // table [@ id ='foo'] / tr | // table [@ id = 'foo'] / tbody / tr 
  

如果您想要一个没有节点集合的表达式：

  // tr [（。| parent :: tbody）[1] / parent :: table [@ id ='foo']] 
  

As in this Stack Overflow answer imagine that you need to select a particular table and then all the rows of it. Due to the permissiveness of HTML, all three of the following are legal markup:

<table id="foo"><tr>...</tr></table>
<table id="foo"><tbody><tr>...</tr></tbody></table>
<table id="foo"><tr>...</tr><tbody><tr>...</tr></tbody></table>

You are worried about tables nested in tables, and so don't want to use an XPath like
table[@id="foo"]//tr.

If you could specify your desired XPath as a regex, it might look something like:
table[@id="foo"](/tbody)?/tr

In general, how can you specify an XPath expression that allows an optional element in the hierarchy of a selector?

To be clear, I'm not trying to solve a real-world problem or select a specific element of a specific document. I'm asking for techniques to solve a class of problems.

解决方案

I don't see why you can't use this:

//table[@id='foo']/tr|//table[@id='foo']/tbody/tr

If you want one expression without node set union:

//tr[(.|parent::tbody)[1]/parent::table[@id='foo']]

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