When displaying timeline information, events and attributes are
described from the point-of-view of the person that is being reported
on. For example, a given marriage may be described as a sister's
marriage or a daughter's marriage, or a father's marriage. It's
the same marriage but the description depends on how the person we're
reporting on is related to the people getting married. This
function takes a reference to an Individual and to a fact, and
describes the latter from the perspective of the former.
However, it will return an empty string if the fact is not one that is
deemed to be a timeline fact for the given Individual. Which
facts count as timeline facts is something that can be configured in
Preferences (General tab).