This hides a comparable function to Cache mode of current
page(s) on/off
except that it applies to all pages of the document
that are not currently visible in the document window. Normally this
icon should remain selected for reasons of speed, because there are
actually only two situations in which the cache data of non-visible
document pages does not correspond to their actual contents: Namely
when you are just editing a frame, virtual copies of which are placed
on other pages – or when you are editing text frames whose
linking is piped across page boundaries.
