Moves example from traps to objects

Since a warning is issued right now, it's not a trap; but some
clarification is needed about precedence of the `but` operator. This
closes #1950 and closes #1953, which was changed before.

doc/Language/objects.pod6

@@ -966,6 +966,19 @@ container. Thus, @-sigiled containers will require binding to make the role
 stick. Some operators will return a new value, which effectively strips
 the mixin from the result.
 
+The operator infix:<but> is narrower than the list constructor. When providing
+a list of roles to mix in, always use parentheses.
+
+=for code
+role R1 { method m {} }
+role R2 { method n {} }
+my $a = 1 but R1,R2; # R2 is in sink context, issues a WARNING
+say $a.^name;
+# OUTPUT: «Int+{R1}␤»
+my $all-roles = 1 but (R1,R2);
+say $all-roles.^name; # OUTPUT: «Int+{R1,R2}␤»
+
+
 Mixins can be used at any point in your object's life.
 
     # A counter for Table of Contents

doc/Language/traps.pod6

@@ -836,18 +836,6 @@ to a power, use parentheses:
 say (-1)²;   # OUTPUT: «1␤»
 say (-1)**2; # OUTPUT: «1␤»
 
-=head2 C<but> in List Construction
-
-The operator infix:<but> is narrower than the list constructor. When providing
-a list of roles to mix in, always use parentheses.
-
-=for code
-role R1 { method m {} }
-role R2 { method n {} }
-my $a = 1 but R1,R2; # R2 is in sink context
-say $a.^name;
-# OUTPUT: «Int+{R1}␤»
-
 =head1 Subroutine and method calls
 
 Subroutine and method calls can be made using one of two forms: