o The -s limit is ARG_MAX - 4K, not ARG_MAX - 2K.

o Mention that the current environment is part of the -s calculation.
o Add a BUGS section that warns against executing a program that increases
  the size of the argument list or the size of the environment.

  I have wondered for a while what the difference is between

    get a big list | xargs sudo command

  which fails and

    get a big list | sudo xargs command

  which succeeds.  The answer is that in the first case, sudo expands
  the environment and pushes the amount of data passed into execve over
  the E2BIG threshold.

usr.bin/xargs/xargs.1

@@ -112,16 +112,17 @@ is 5000.
 .It Fl s Ar size
 Set the maximum number of bytes for the command line length provided to
 .Ar utility .
-The sum of the length of the utility name and the arguments passed to
+The sum of the length of the utility name, the arguments passed to
 .Ar utility
 (including
 .Dv NULL
-terminators) will be less than or equal to this number.
+terminators) and the current environment will be less than or equal to
+this number.
 The current default value for
 .Ar size
 is
 .Dv ARG_MAX
-- 2048.
+- 4096.
 .It Fl t
 Echo the command to be executed to standard error immediately before it
 is executed.
@@ -164,10 +165,19 @@ If any other error occurs,
 exits with a value of 1.
 .Sh SEE ALSO
 .Xr echo 1 ,
-.Xr find 1
+.Xr find 1 ,
+.Xr execvp 3
 .Sh STANDARDS
 The
 .Nm
 utility is expected to be
 .St -p1003.2
 compliant.
+.Sh BUGS
+If
+.Ar utility
+attempts to envoke another command such that the number of arguments or the
+size of the environment is increased, it risks
+.Xr execvp 3
+failing with
+.Dv E2BIG .