Simplify stylesheets by changing the context node.
通过修改上下文节点简化样式表。
If let appears outside rule, its value is computed with the document root as context node.
如果let出现在rule之外，其value以文档根作为上下文节点计算得到。
The expression is evaluated with respect to a certain context node, which in this case is the entire document.
表达式是针对特定的上下文节点计算的，在这个例子中是整个文档。
The context node for this XPath expression is the element that the template is replacing — in this case, an ATOM element.
这个XPath表达式的上下文节点是模板替换的元素，在这里是ATOM元素。
To select some parts of a document, you specify a path between a starting node (called the context node) and the contents to be selected.
要选择文档的某一部分，必须规定起始节点(称为上下文节点)和所选内容之间的路径。
Accessing the context node is most common.
访问上下文节点是最常见的。
A location path selects a set of nodes relative to the context node.
定位路径选定相对于上下文节点的一个节点集合。
By default, all parent and ancestor nodes above the current context node are displayed.
默认情况下，会显示当前上下文节点上面的所有父节点和祖先节点。
Recall that once the initial context has been specified, all later search operations take place within the child nodes of that initial context node.
回想一下，当指定了初始上下文后，稍后将在该初始上下文节点的子节点内进行所有的搜索操作。
Following an axis from a context node will still return nodes in document order, but once it has those nodes, your stylesheet can reorder them as it requires.
虽然从上下文节点出发沿着某个轴仍然只能按照文档顺序返回节点，但是得到节点之后样式表可以根据需要重新排列节点。
To evaluate XPath expressions, passed as simple String objects, given a particular node in an instance of the supported data model to act as the context node.
要计算XPath表达式，将表达式作为简单的String对象传递，并给定所支持的数据模型实例中的某个节点作为上下文节点。
To evaluate XPath expressions, passed as simple String objects, given a particular node in an instance of the supported data model to act as the context node.
要计算XPath表达式，将表达式作为简单的String对象传递，并给定所支持的数据模型实例中的某个节点作为上下文节点。
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