How XPath 1.0 comparisons and negatiations work, since I always forget

Where $node-set is bound to a node-set having two or more nodes, and $string bound to a string, evaluating an expression will return a boolean true, if:

$node-set = $string

there is a node in $node-set that is equal to $string

$node-set != $string

there is a node in $node-set that is not equal to $string

not($node-set = $string)

there is not a node in $node-set that is equal to $string

not($node-set != $string)

there is not a node in $node-set that is not equal to $string

How parenthesis change expression evaluation:

descendant::*[1] or (descendant::*)[1]

Closest descendant element

descendant::*[last()] or (descendant::*)[last()]

Most distant descendant element

ancestor::*[1] or (ancestor::*)[last()]

Closest ancestor element

ancestor::*[last()] or (ancestor::*)[1]

Most distant foo ancestor element

Rewrites of some expressions I've seen in stylesheets to eliminate the last() function.

(ancestor::*/@role)[last()] = 'child' or
(ancestor::*/@role)[last()] = 'descendant'

ancestor::*[@role][1]/@role[. = 'child' or
                            . = 'descendant']