A path that is a single forward-axis step from one context node returns its
nodes already in document order with no duplicates, so the document-order
sort is redundant. AxisNavigation produces the structural forward axes
(child, descendant, descendant-or-self, self, following, following-sibling)
in document order, deriving sibling order from the same children array the
order key compares, so the two can never disagree. This is the common shape
after //x compiles and fuses to a single descendant::x step.
The attribute axis (whose order interleaves with namespace declarations), the
namespace axis (produced in dictionary order), and every reverse axis
(nearest-first) are excluded and still sorted. Measured xpath ~7% faster on
the 20k-item generated corpus via a same-state A/B, identical results.
XPathSingleStepOrderTests pins document order for each included axis, that the
reverse axes still normalize, and that multi-step paths still sort. An
adversarial order-correctness review found no query whose order or uniqueness
the change breaks.
Mihaela Mihaljevic
5ad3cf10fc