Reflowed some over-long ones, fixed some typos, capitalise starts of
sentences (and end them with suitable punctuation). Removed one as
redundant, made another pair redundant by changing the code (use an
overt NaN instead of commenting that it's happening). Prefer C++-style
when single-line. Don't pretend to be QDoc comments, or have other
eccentricities about start-markers.
Change-Id: I5a30e1b22a08866124f09060bb35f5bd27cd443b
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
e94b579679