doc: Periodic grammarcheck of documentation. * doc/interpreter/basics.txi, doc/interpreter/container.txi, doc/interpreter/contrib.txi, doc/interpreter/diagperm.txi, doc/interpreter/errors.txi, doc/interpreter/install.txi, doc/interpreter/sparse.txi, libinterp/corefcn/ellipj.cc, libinterp/corefcn/mappers.cc, libinterp/corefcn/regexp.cc, libinterp/corefcn/tril.cc, libinterp/dldfcn/__init_fltk__.cc, libinterp/dldfcn/fftw.cc, libinterp/interpfcn/dirfns.cc, libinterp/interpfcn/input.cc, libinterp/octave-value/ov-fcn-inline.cc, libinterp/octave-value/ov-struct.cc, scripts/@ftp/cd.m, scripts/general/interp1.m, scripts/general/num2str.m, scripts/image/ind2rgb.m, scripts/image/rgb2ind.m, scripts/io/importdata.m, scripts/io/textread.m, scripts/java/javamem.m, scripts/linear-algebra/condest.m, scripts/linear-algebra/onenormest.m, scripts/miscellaneous/error_ids.m, scripts/miscellaneous/getfield.m, scripts/miscellaneous/setfield.m, scripts/plot/area.m, scripts/plot/pcolor.m, scripts/plot/stairs.m, scripts/set/powerset.m, scripts/sparse/bicg.m, scripts/sparse/bicgstab.m, scripts/sparse/cgs.m, scripts/specfun/ellipke.m, scripts/special-matrix/gallery.m, scripts/strings/strjoin.m, scripts/strings/strsplit.m, scripts/testfun/__have_feature__.m, scripts/testfun/__printf_assert__.m, scripts/testfun/__prog_output_assert__.m, scripts/testfun/__run_test_suite__.m: grammarcheck documentation.

--- a/scripts/plot/area.m
+++ b/scripts/plot/area.m
@@ -25,9 +25,9 @@
 ## @deftypefnx {Function File} {} area (@var{h}, @dots{})
 ## @deftypefnx {Function File} {@var{h} =} area (@dots{})
 ## Area plot of the columns of @var{y}.  This shows the
-## contributions of each column value to the row sum.  It is functionally similar to
-## @code{plot (@var{x}, cumsum (@var{y}, 2))}, except that the area under
-## the curve is shaded.
+## contributions of each column value to the row sum.  It is functionally
+## similar to @code{plot (@var{x}, cumsum (@var{y}, 2))}, except that the
+## area under the curve is shaded.
 ##
 ## If the @var{x} argument is omitted it defaults to 
 ## @code{1 : rows (@var{y})}.  A value @var{lvl} can be defined that determines
@@ -44,10 +44,12 @@
 ## Example: Verify identity sin^2 + cos^2 = 1
 ##
 ## @example
+## @group
 ## t = linspace (0, 2*pi, 100)';
 ## y = [sin(t).^2, cos(t).^2)];
 ## area (t, y);
 ## legend ('sin^2', 'cos^2', 'location', 'NorthEastOutside');  
+## @end group
 ## @end example
 ## @seealso{plot, patch}
 ## @end deftypefn