What Is Meant by "Context Node" in XPath?

In xpath, the term "context node" refers to the node in an XML/HTML document that is currently being evaluated or processed by a xpath expression.

When a xpath expression is executed, it always starts from a context node, and then uses one or more "axes" and "node tests" to navigate through the document and select specific nodes. The context node serves as a starting point for this navigation, and all subsequent steps in the xpath expression are taken relative to the context node.

For example, let's suppose you have the following XML document:

<blog>
  <post category="css">
    <title>What Is CSS Pseudo-Class?</title>
    <published>2021-09-18 17:30:00</published>
  </post>
  <post category="html">
    <title>What Is an HTML Entity?</title>
    <published>2021-06-26 00:00:00</published>
  </post>
</blog>

You could, for example, use the following expression to select the title of the first blog post in the "css" category:

/blog/post[@category='css'][1]/title

In this example, the context node is initially set to the root element of the document, and then is updated as the expression is evaluated. This means that the context node starts at the top-level element (i.e. <blog>), and then changes to the selected <post> element, and then to its child <title> element, as it navigates through the hierarchy of the document.

Understanding the concept of the context node is important for writing effective and accurate xpath expressions, as it determines the starting point and scope of the selection process. By carefully selecting and manipulating the context node, you can target specific nodes within an XML/HTML document, and extract the information that you need.