Point out difference in where clause...

...between block and non-block versions.

RT#131239: https://rt.perl.org/Ticket/Display.html?id=131239

Author: zoffixznet

doc/Type/Signature.pod6

@@ -139,6 +139,21 @@ The first of those can be shortened to
 i.e., you can use a literal directly as a type and value constraint
 on an anonymous parameter.
 
+B<Tip:> pay attention to not accidentally leave off a block when you,
+say, have several conditions:
+
+  -> $y where   .so && .name    {}( sub foo {} ) # WRONG!!
+  -> $y where { .so && .name }  {}( sub foo {} ) # OK!
+  -> $y where   .so &  .name.so {}( sub foo {} ) # Also good
+
+The first version is wrong and will issue a warning about sub object coerced
+to string. The reason is the expression is equivalent to
+C<($y ~~ ($y.so && $y.name))>; that is "call C<.so>, and if that is C<True>,
+call C<.name>; if that is also C<True> use its value for smartmatching…". It's
+the B<result> of C<(.so && .name)> is will be smartmatched against, but we
+want to check that both C<.so> and C<.name> are truthy values. That is why
+an explict Block or a L<Junction> is the right version.
+
 All previous arguments that are not part of a sub-signature in a C<Signature>
 are accessible in a C<where>-clause that follows an argument. Therefore,
 the C<where>-clause of the last argument has access to all arguments of a