Returns the base URI of a node.

The zero-argument form of this function is deterministic, context-dependent, and focus-dependent.

The one-argument form of this function is deterministic, context-independent, and focus-independent.

The zero-argument version of the function returns the base URI of the context node: it is equivalent to calling fn:base-uri(.).

The single-argument version of the function behaves as follows:

1. If $arg is the empty sequence, the function returns the empty sequence.
2. Otherwise, the function returns the value of the dm:base-uri accessor applied to the node $arg. This accessor is defined, for each kind of node, in the XDM specification (See ).

As explained in XDM, document, element and processing-instruction nodes have a base-uri property which may be empty. The base-uri property for all other node kinds is the empty sequence. The dm:base-uri accessor returns the base-uri property of a node if it exists and is non-empty; otherwise it returns the result of applying the dm:base-uri accessor to its parent, recursively. If the node does not have a parent, or if the recursive ascent up the ancestor chain encounters a parentless node whose base-uri property is empty, the empty sequence is returned. In the case of namespace nodes, however, the result is always an empty sequence — it does not depend on the base URI of the parent element.

See also fn:static-base-uri.