Rather than using order to specify item precedence, we now construct
a set of menu items for each element traversing upward from the target.
When merging items for a given element, we pass the specificity to the
merge function, which uses it to decide whether or not to clobber
existing items. When assembling the overall menu, we don’t ever clobber
to ensure that items added for elements closer to the target always win
over items matching further up the tree.
eb929cb7a2