Height Identity
Gets and then puts back image height. Images should not be squished or vanished as a result. The second image uses the border-box model, which is the only possibility in IE quirks mode (and available to all with CSS3). The third has an odd, but valid border rule.
Query Compatibility
Queries should filter user input (or not) consistently. If not filtered, the query engine is incompatible with QSA and XPath implementations. Check/uncheck and select and then refresh the document to see the results (most UA's preserve user input).
Can it Find a Single Image Map?
Apparently not in several versions (and modes) of IE.
Can it Find the One Link with a Specified Tab Index?
Not consistently, not even in IE8 (click the compatibility mode button).
Has explicit tab index Has no explicit tab index