2) Handling Webviews: While studying advertisements, we
faced a significant challenge: most of the in-app advertisements
are implemented as customizations of Webviews (these are
special widgets that render Web content, i.e., HTML, JavaScript,
and CSS). Webviews and some custom widgets are opaque in
the UI hierarchy obtained from the system, i.e., the UI rendered
inside them cannot be observed in the native UI hierarchy and
thus interaction with them will be limited. To the best of our
knowledge, previous research has not proposed a satisfactory
solution to this problem