Path expressions

A path expression consists of one or more steps that are separated by slash (/) or double-slash (//) characters. A path expression can begin with a step or with a slash or double-slash character. Each step before the final step generates a sequence of nodes that are used as context nodes for the step that follows.

The first step specifies the starting point of the path, often by using a function call or variable reference that returns a node or sequence of nodes. An initial "/" indicates that the path begins at the root node of the tree that contains the context node. An initial "//" indicates that the path begins with an initial node sequence that consists of the root node of the tree that contains the context node, plus all of the descendants of the root node.

Each step is executed repeatedly, once for each context node that is generated by the previous step. The results of these repeated executions are then combined to form the sequence of context nodes for the step that follows. Duplicate nodes are eliminated from this combined sequence, based on node identity.

The value of the path expression is the combined sequence of items that results from the final step in the path. This value can be either a sequence of nodes or a sequence of atomic values. Because each step in a path provides context nodes for the step that follows, the final step in a path is the only step that can return a sequence of atomic values. A path expression that returns a mixture of nodes and atomic values results in an error.

The node sequence that results from a path expression is not guaranteed to be in a specific order. To understand when a path expression returns ordered results, see the topic that describes the order of results in XQuery expressions.