XPath 中的 // 和 .// 有什么区别？

Question

When I execute these XPath expression on Chrome Developer Tools' console over google.com, I got the same results

• $x("(.//*[@id='gs_lc0'])")

• $x("(//*[@id='gs_lc0'])")

What is the usage of dot in XPath?

Answer 1

In XPath, // and .// are both syntactic abbreviations:

• // is short for /descendant-or-self::node()/
• .// is short for self::node()/descendant-or-self::node()/

The descendant-or-self axis contains the context node and all descendents of the context node. So the difference between // and .// reduces to a difference in context nodes.

For // , the context node is the root node; // is an absolute location path .

For .// , the context node depends upon the context; .// is a relative location path . At the top-level evaluation in Google Developer Tools console, the context node is the root node, so you'll see identical results.

In short:

• Use // when you wish to select nodes from the entire document.
• Use .// when you wish to select nodes only beneath the context node.