Hopefully improve SUB-MAIN-OPTS doc

Author: lizmat

doc/Language/functions.pod6

@@ -877,17 +877,22 @@ call L<exit|https://docs.perl6.org/routine/exit>.
 =head2 C<%*SUB-MAIN-OPTS>
 
 It's possible to alter how arguments are processed before they're passed
-to C<sub MAIN {}> by setting options in C<%*SUB-MAIN-OPTS> hash. Available
-options are:
-
-=head3 C<named-anywhere>
-
-    (my %*SUB-MAIN-OPTS)<named-anywhere> = True;
+to C<sub MAIN {}> by setting options in C<%*SUB-MAIN-OPTS> hash.  Due to the
+nature of dynamic variables, one needs to set up its own C<%*SUB-MAIN-OPTS>
+hash and fill it with the appropriate settings.  For instance:
+
+    my %*SUB-MAIN-OPTS =
+      :named-anywhere,    # allow named variables at any location
+      :!foo,              # don't allow foo
+    ;
     sub MAIN ($a, $b, :$c, :$d) {
         say "Accepted!"
     }
 
-I«Note the use of parentheses around C<(my %*SUB-MAIN-OPTS)>».
+Available options are:
+
+=head3 C<named-anywhere>
+
 By default, named arguments to the program cannot be given after any positional
 arguments are specified. However, if C«%*SUB-MAIN-OPTS<named-anywhere>» is
 set to a truthy value, named arguments can be specified anywhere, even after