Elaborate on the "my Foo .= new()" idiom

Author: lizmat

doc/Language/5to6-perlop.pod6

@@ -204,12 +204,24 @@ $x = $ok ?? $yes !! $no;  # Perl 6
 Although not fully documented, S03 indicates that the mathematical and
 logical assignment operators should work as you would expect. The one
 noticeable change is that C<.=> calls a mutating method on the object on
-the left, while C<~=> is the string concatenation assignment, as you
-might expect with the changes in C<.> and C<~>. Also, the bitwise
-assignment operators are likely not separated into numeric and string
-versions (C<&=>, etc., vs. C<&.=>, etc.), as that feature is currently
-experimental in Perl 5 itself - although, again, this is not
-specifically documented.
+the left (which can also be a type-object).  This allows for the following
+useful idiom:
+
+=begin code
+class LongClassName {
+    has $.frobnicate;
+}
+my LongClassName $bar .= new( frobnicate => 42 ); # no need to repeat class name
+=end code
+
+This ensures that C<$bar> will only be able to contain a C<LongClassName>
+object, as well not having to repeat (and possibly misspell) the class name.
+
+C<~=> is the string concatenation assignment, as you might expect with the
+changes in C<.> and C<~>. Also, the bitwise assignment operators are likely
+not separated into numeric and string versions (C<&=>, etc., vs. C<&.=>, etc.),
+as that feature is currently experimental in Perl 5 itself - although, again,
+this is not specifically documented.
 
 =head2 Comma Operator