If you feed a really, really long string into Xft, it will cause an
error because the maximum request length will be violated.
Xft should cover this up and automatically break long strings into
multiple pieces... while drawing really long strings is pathological
it's a lot of work for an app to check everywhere that a user didn't
give it such.
(Doesn't affect Pango because Pango limits requests to 1024 glyphs,
but it would affect a native user of the Xft API.)