Descending Along Branches

Sometimes you want the XPath processor to evaluate all nodes that are descendants of a node and not just the immediate children of that node. This amounts to operating on a branch of the tree that forms the document.

To specify the evaluation of descendants that starts at the root node, insert two forward slashes (//) at the beginning of a query.

To specify the evaluation of descendants that starts at the context node, insert a dot and two forward slashes (.//) at the beginning of the query.

Following is a query that finds all last-name elements anywhere in the current document:

 //last-name 

The // selects from all descendants of the context node set. For example:

book//award 

For the sample bookstore data, the following two queries are equivalent. Both return all last-name elements in the document.

//last-name 
//author//last-name 

Tip:// is useful when the exact structure is unknown. If you know the structure of your document, avoid the use of //. A query that contains // is slower than a query with an explicit path.