fn:outermost

fn:outermost($nodes as node()*) as node()*

This function is deterministic, context-independent, and focus-independent.

The effect of the function call fn:outermost($nodes) is defined to be equivalent to the result of the expression:

$nodes[not(ancestor::node() intersect $nodes)]/.

That is, the function takes as input a sequence of nodes, and returns every node within the sequence that does not have another node within the sequence as an ancestor; the nodes are returned in document order with duplicates eliminated.

The formulation $nodes except $nodes/descendant::node() might appear to be simpler, but does not correctly account for attribute nodes, as these are not descendants of their parent element.

The motivation for the function was based on XSLT streaming use cases. There are cases where the [XSLT 3.0] streaming rules allow the construct outermost(//section) but do not allow //section; the function can therefore be useful in cases where it is known that sections will not be nested, as well as cases where the application actually wishes to process all sections except those that are nested within another.

If the source document contains nested sections represented by div elements, the expression outermost(//div) returns those div elements that are not contained within further div elements.