trueif the element or one of its ancestors is the specified element, and
isntreverses the result.
open element (of element-expression)? (is | isnt) namespace-modifier? (element-name | element-name-list)
open element is tests whether the element stack of the currently-active parse contains an instance of the
element element-name, or one of the elements listed in element-name-list. element-name-list is a parenthesized list of elements, separated by
isnt will reverse these results.
If element-expression is not specified, the test searches the element stack starting with the current element. If element-expression is specified, the search begins with the element specified by element-expression.
You can specify the name dynamically by using the identity operator (
~) followed by a
string expression: for example,