Hit-testing for pointer events

I was glancing at the specification tonight and ran across a section 
detailing touch-action:

"When a user touches an element, the effect of that touch is determined 
by the value of the |touch-action| property and the default touch 
behaviors on the element and its ancestors. To determine the effect of a 
touch, find the nearest ancestor (starting from the element itself) that 
has a default touch behavior."

I'm curious what exactly the specification means by "touches an element" 
or "nearest ancestor", especially given touch events may occur over a 
area rather than only occurring at a single point. Is it worth 
specifying a behavior for finding elements near a touch (either within 
the touch radius or using a fuzzy constant around the center of the 
touch point)?