您针对这个对象运行一个正则表达式，提取用户代理字符串。

You run a regular expression against it to extract the user agent string.

youdao

因此，建立这种联系后，还需要获得一个能够处理XPath表达式求值的对象。

So with that link established, you need to get an object that can handle XPath expression evaluation.

youdao

对于那些只使用1到2个正则表达式的小型的应用程序，这意味着没有必要每次都创建一个Regex对象。

For those little utility applications that only use one or two expressions, this means explicitly creating a RegEx object is probably not necessary.

youdao

I just want to remind you, if I wanted to, for example, type in an expression like that, notice the syntactical form, it's an expression, a number, followed by an operand, followed by another expression.

我想要提醒下大家，如果你想要，例如，输入一个这样的表达式，注意语法形式，这是个表达式，一个数字，后面是一个运算对象，后面是另外一个表达式。

麻省理工公开课 - 计算机科学及编程导论课程节选