Querying with the expression language

• Used in multiple ways: as a pattern; to navigate within input and output trees; to access content of source document
• Node data-type represents node in tree
• Functions to access node properties
• Functions to access node children, parent, attributes, owner, preceding siblings, following siblings
• Node-set data-type represents result of a query
• Node-sets may but need not be totally ordered
• Functions to return node-set containing subtree rooted at a node
• Functions to select matching members from a node-set
• Function to count members of node-set
• Function to return first member of a node-set
• Implemented lazily