For example, a sample documentation page from Apple's site has
thousands of child elements containing the components of the page,
which itself spans many, many scroll lengths (i.e. a scroll amount
which would move the entirety of a given span of content out of view).
In this case, traversing the group members requires a huge amount of
processing and copying (it takes my Core 2 duo machine up to 99% CPU
for 10 seconds for the single page). It is simply impractical for me
to traverse the widgets.